@fabienismyfriend

Your galleries seem to be working as expected when I view them on mobile devices.
If a mobile device has been detected and the gallery is embedded on a web page with dimensions of less than 100% x 100% or if there is other content on the page (i.e. if the gallery is not the only element on the page and does not take up the full page), then the Splash Page will be displayed.
The Splash Page is a placeholder for the gallery which, when tapped, will expand the gallery on a new page of its own (to give the gallery more space).
By default, the Splash Page displays the first image in the gallery. You can change this to any image you like using the splashImageUrl configuration option (in JuiceboxBuilder-Pro's 'Customize -> Splash Page' section).

There are a few things you could try.

(1) If you simply do not want the Splash Page to appear, then you can set showSplashPage="NEVER" ('Customize -> Splash Page').
(2) Additionally, if you want the Large Screen Mode version of your gallery to be displayed on all devices, then you can set screenMode="LARGE" ('Customize -> General') but please bear in mind that some gallery elements may appear too small on mobile devices.

You could avoid the problem by ensuring that your gallery is the only element on your web page and that its dimensions are 100% by 100%.
Currently, your gallery has a height of 92% and there is a table on the page alongside the gallery.
If you were to remove the table and change the height of the gallery to 100%, then the gallery would fill the page and the Splash Page would not appear (but the gallery would still be displayed in Small Screen Mode on mobile devices which would be beneficial when viewing on small screens).

I'd recommend using the 'index.html' page from a gallery built with JuiceboxBuilder-Pro as a template (where the gallery is the only element on the page).

Also, if you check your current gallery's embedding page with the W3C Markup Validation Service, you'll see that there are some HTML errors on the page (such as a missing </body> tag at the end of the file). The info entries do not need attention but the errors really ought to be fixed.
If a web page does not contain valid HTML code, then the web page might be rendered by the browser in an unpredictable manner. Some browsers are more tolerant towards errors than others but if the code on the page is valid (i.e. no errors), then you can be sure that the page will display with consistency across all browsers.

I hope these notes point you in the right direction.

Perhaps the two most influential factors in the loading of a gallery are the speed of the web server (where the gallery files are hosted) and the user's internet connection. Unfortunately, there is little you can do about either of those.

You could maybe tweak the size of your images. From memory, if you allow JuiceboBuilder-Pro to resize your images at default settings (medium sized images at 1024 x 768), the resulting images tend to be around 120KB each. This is significantly smaller than your current average of 300KB and images should, therefore, load faster (and they should still hopefully be of a reasonable quality for web gallery use).
You could also take advantage of Juicebox-Pro's Multi-Size Image Support (see here for details) where the gallery stores different sizes of images and serves up smaller ones on mobile devices. It might make a difference (depending on factors such as the device's screen size and pixel density).

I don't think the imageScale mode will make a big difference to the loading speed but the imagePreloading value (Large Screen Mode only) might. (Both of these configuration options can be found in the Main Image Options section here). When setting the preloading to the default value of PAGE, Juicebox will preload all images on the current thumbnail page so reducing the number of thumbnails per page should speed up the initial load a bit. Alternatively, you could set the preloading to NEXT, whereby only the next image in the gallery is preloaded. This should provide the fastest possible loading time (less initial burden on the browser) but I can't say whether it will make a difference on your Android device. It's something you can experiment with, though.

Unfortunately, the Juicebox module for Drupal is an unofficial plugin which was not written by ourselves and we have little knowledge of it.

I notice that the latest release is an alpha version (4.00-alpha2) so perhaps the current maintainers released a version with basic functionality and plan to add to it later (although this is just speculation on my part).

Maybe you could post in the Juicebox Issues section of the Drupal forum (here) where the maintainers might be able to give you more information.

I know this does not directly answer your question or resolve the issue but I hope that it at least points you in the right direction.

Perhaps some other Drupal users can post here with more information, too.

Filezilla 3.69.1 works fine (uploads all files inside the 'jbcore' folder) on my Windows 11 PC. Tested on a fresh gallery created with JuiceboxBuilder-Pro v1.5.1.2 and Filezilla 3.69.1 with all default settings. Even after changing the attributes of the 'jbcore' folder to hidden (including all subfolders and files), dragging and dropping the gallery folder into Filezilla uploaded everything, including the 'jbcore' folder and all its contents.

I doubt that any errors in a file would prevent a file from being uploaded (via FTP or SFTP). Filezilla (for example) does not check files for style or syntax errors. it just uploads what it's given.
Likewise, I doubt a web server would check files for problems. If a file had any errors in it, the first anyone would likely know about it is if the file is opened in a browser (and then the browser could potentially choke on the error).

It's not really an error. It's just three lines of CSS code which contain browser-specific prefixes (so that the 'transform' can be performed in all browsers).
Any line of CSS code that is not recognised by a browser might be flagged with a warning (by the browser) but the browser ought to just ignore the line of code that it does not understand and then carry on parsing the file.
These days, all major browsers should recognise 'transform' and so the code now could be replaced by:

... or, for backwards compatibility with older browsers:

I'm not sure that your solution is best as it's not actually valid CSS.
Try entering the original code into the W3C CSS Validation Service and you'll see that the code is valid.
However, try validating your code and you'll see errors reported.

I'm really not sure why your gallery is not loading with the untouched CSS file. As I mentioned above, I think it's more likely to be your browser that your FTP/SFTP program or web server. What browser and version are you using?

However, if for whatever reason your browser does not like the original (valid) CSS code, try:

... instead. It should work just fine (in a modern browser).

I hope you get on OK.
You could try re-uploading your gallery before contacting your web host (in case something happened during the original upload resulting in missing files). This might be enough to resolve your problem.
However, if this does not help, then maybe your web host could shed some light on things.
Just for the record, it looks like the entire jbcore folder is missing. Maybe it has been uploaded to a different location and the path to the juicebox.js file in your gallery's embedding code needs to be adjusted? Just a thought.

It's not possible to change the installation directory or the working folder (the hidden .tempGallery folder) but you can save and load galleries to and from any location you like (it does not need to be the Desktop).

The installation directory should not really be a problem (iCloud will not, be default, be backing up installed applications) and the fact that gallery folders can be moved (manually by the user) to a location not being synced means that iCloud can be worked around here, too.

The problem seems to be the location of the working folder which JuiceboxBuilder puts in the Documents folder which is a folder commonly synced by iCloud (and other similar services). Competing applications both trying to work on the same folder at the same time is most likely the issue.

Unfortunately, JuiceboxBuilder hard-codes the location of the working folder within its code and it is not user-changeable.
Ensuring that the Documents folder is not being synced (or, more specifically, the JuiceboxBuilder-Lite or JuiceboxBuilder-Pro subfolder within the Documents folder) is the best solution we have at present.

If I use just the configuration options shown in your post, the thumbnails in my test gallery are positioned at the bottom as expected.

Please check your gallery's 'config.xml' file to see if there are any other configuration options being set which might account for the gallery layout you are seeing.

Also, check to see if there is any custom CSS on your gallery's embedding page which is perhaps overriding the gallery's own CSS and interfering with its layout.

If you continue to experience difficulties, please post the link to your gallery so that I can examine your gallery and its embedding page. (If you don't want to post it publicly here in the forum, you can email it to me at steven@juicebox.net.)
Once I'm able to see the gallery live on your web server, I should hopefully be able to determine the cause of the problem and propose a solution.
(Just for the record, there are no known bugs with thumbsPosition but without knowing exactly what is causing your problem, I can't rule it out.)

Thanks!

@nono

If your problem is that you're live preview obscures other content within JuiceboxBuilder and you truly are using the latest version of AIR (v51), then the version of AIR is the problem.
You'll need to use the most recent version of AIR which has support for WebKit (the embedded browser that JuiceboxBuilder uses for the live preview). This is currently AIR v33.1.1.744. It can be downloaded from the foot of the AIR download page: https://airsdk.harman.com/runtime

Please uninstall AIR v51 first before installing AIR v33.1.1.744.
Please see this forum post for further details: https://juicebox.net/forum/viewtopic.php?id=5319

I hope this helps to resolve your problem.

The "trailing slash on void elements" messages are listed on the W3C Markup Validation site as "Info" (rather than "Warning" or "Error"). As such, the messages are just informational and should not cause any problems.
Trailing slashes on void elements are optional in HTML 5 and can, indeed, interact badly with unquoted attribute values but Juicebox does not use any unquoted attribute values (all attribute values in the code generated by Juicebox-Pro are quoted) so the trailing slashes are fine (although unnecessary) in this scenario.
I cannot be 100% sure how Google's SEO crawling and indexing works but as the trailing slashes are valid HTML 5, there should not be any problems with SEO or anything else.

[Conversation continued via email. No Problem with gallery. I'll post back here if a solution to the problem is found.]

@jerryfields

I'm sorry to hear that you are having trouble with JuiceboxBuilder-Pro on your Mac.
I wish I could be of more help but it sounds like you might already have tried everything that I'm aware of.

Over the years, I've been able to collate all the problems and solutions that users have run into and I've documented them here in the forum.

You've no doubt seen and tried most of (if not all) the suggestions but, for the sake of completeness, here are the two threads/posts I think might be most relevant to your problem.
Unresponsive New Gallery and Open Gallery buttons in JuiceboxBuilder - https://juicebox.net/forum/viewtopic.php?id=5295
Troubleshooting JuiceboxBuilder installation and usage problems - https://juicebox.net/forum/viewtopic.php?id=5114

It's also worth noting that you'll need to be using AIR v33.1.1.744 (and not the latest version, AIR v51. See here for details: https://juicebox.net/forum/viewtopic.php?id=5318

Also, if you have a Mac which uses Apple Silicon (M1, M2, M3, M4 hardware), you may need to open JuiceboxBuilder-Pro using Rosetta.
This is noted as a Known Issue for Mac users on the AIR download page: https://airsdk.harman.com/runtime

It's also mentioned here in our forum (with instructions and further links): https://juicebox.net/forum/viewtopic.php?id=5289
Here is the Apple support page regarding Rosetta 2: https://support.apple.com/en-us/102527

I don't think the AIR or Rosetta issues will be relevant to your problem (I don't think you'd have made it as far as JuiceboxBuilder-Pro's 'Start' panel otherwise) but I thought I should mention it.

Once again, I'm sorry I don't have a definitive answer for you but maybe other Mac users reading this can chip in and help out.
If I think of anything else that might help, I'll be sure to post back to let you know.