Please make sure that you are using the latest version of Juicebox (v1.4.3.2).
Flickr made a change to their API to be more secure and we updated Juicebox to handle this change in v1.4.2.
Please see this Juicebox blog entry for further information.

If you are already using the latest version of Juicebox, then the issue might be caused by a temporary glitch with Flickr's web servers or a problem with your internet connection. Either might be preventing your browser from being able to download the images in a timely manner resulting in blank spaces where images should be.

Please post the URL to your gallery's web page so that I can take a look at the problem and investigate further.
I will report back with my findings.

As far as I am aware, there are currently no plans to add support for sharing on Instagram.

If you wanted to add support for a social media platform which is not currently supported by Juicebox, then you might be able to implement it using the Juicebox-Pro API.
As long as the social media platform has its own sharing functionality (where you can send information to their web site via a share URL), then you could manually add an HTML button to your web page (alongside your gallery) which, when clicked, would fetch the required information about the image currently being displayed in the gallery (using the available Juicebox-Pro API methods such as getImageInfo()) and use this information to populate the parameters in the share URL.
Knowledge of HTML and JavaScript would be required and while this may be possible, it might not be easy to achieve (although I hope it points you in the right direction if you plan to try it).

JuiceboxBuilder-Pro's 'Add SEO Content' functionality adds SEO code to the gallery's 'index.html' file (and to the embedding code presented on the 'Publish' tab which you can copy and paste if you want to embed your gallery into an existing web page alongside other content).

The SEO code is not included in the HTML code which is generated dynamically by the 'juicebox.js' file when the gallery is displayed.

The SEO code is included in the embedding code (inside the 'juicebox-container' <div>) so that it can be seen by web bots crawling the internet and also by viewing the source of the web page in a browser (but not by inspecting the dynamically generated code via a browser's developer tools).

'Add SEO Content' is a feature of JuiceboxBuilder-Pro only. The SEO code must be generated whist creating the gallery and before the gallery can be displayed. As such, 'Add SEO Content' is not a configuration option that can be added to a gallery's XML file. (It is used only by JuiceboxBuilder-Pro when creating a gallery and is not recognised by the 'juicebox.js' file when a gallery is displayed.)

I hope this helps to clarify things.

[Post moved to keep cases separate.]

I can't explain how your web address was used as the linkURL in several (but not all) of the images in your gallery but I'm glad that you have been able to resolve your problem. Thank you for posting back to let me know.

Just for the record, linkURLs can be entered (and deleted) on the 'Images' tab of JuiceboxBuilder-Pro.
Click a thumbnail and the Title, Caption and Link URL input fields for that particular image will be displayed.

If you wanted to remove all linkURLs from a gallery's XML file, you could open the file in a text editor which supports regular expressions, (such as Notepad++), do a global regular expression search for the following:

linkURL=".*?"

... and replace all instances found with:

linkURL=""

This will replace all linkURLs with linkURL="" in a single action and imageURLs will be used for all images.

Please note that we did not write the Juicebox module for Drupal and, as such, support for the module would be better directed towards the Drupal forum where the author of the module (who is more familiar with both Drupal and the module itself) should be able to answer your query: https://www.drupal.org/forum
The author of the module is active in the Drupal forum (and very helpful) and should be able to help you out.
The Drupal forum would definitely be the best place for you to post your query.
I realise that this does not directly answer your query but it should at least point you in the right direction.

The problem is due to linkURL entries in your gallery's XML file such as the following:

linkURL="www.paulraphaelson.com"

If a linkURL is present, then Juicebox will use this instead of the imageURL when the Open Image Button is clicked.
Because your linkURL does not start with http://, Juicebox sees the path as being relative (to the HTML page containing the gallery's embedding code).

Try one of the following:
(1) Change your linkURLs to be the same as your imageURLs (and the images will be opened when the Open Image button is clicked).
(2) Leave your linkUR s empty (and Juicebox will use the imageURLs). (Same result as #1 above.)
(3) Change your linkURLs from www.paulraphaelson.com to http://www.paulraphaelson.com and when the Open Image Button is clicked, the user's browser will open the address http://www.paulraphaelson.com.

Use relative paths in your embedding code and the gallery should display both locally (in supported browsers - please see this FAQ for details) and online.

For example:

<!--START JUICEBOX EMBED-->
<script src="../../Benutzer/ThomasKlinger/Bilder/galerie/jbcore/juicebox.js"></script>
<script>
    new juicebox({
        baseUrl : '../../Benutzer/ThomasKlinger/Bilder/galerie/',
        containerId : 'juicebox-container',
        galleryWidth : '800',
        galleryHeight : '600',
        backgroundColor: '#222222'
    });
</script>
<div id="juicebox-container"></div>
<!--END JUICEBOX EMBED-->

The above is just an example. I do not know the file structure of your site so you will need to make sure that the relative paths are correct.

Just for the record, if you added 'file:///' to the beginning of your paths, your gallery might work locally but it would not work online as visitors to your web site would not have access to files on your C:/ drive.
For example:

<script src="file:///C:/Benutzer/ThomasKlinger/Bilder/galerie/jbcore/juicebox.js"></script>

No problem.
Hopefully you'll be able to sort things out. It certainly looks like the problem is related to file or folder permissions on your web server.
If you continue to experience difficulties, I'm still happy to take a look for you so just let me know.

Thank you for sharing your findings.
Unfortunately, I cannot explain why JuiceboxBuilder-Pro cannot write back to the original gallery folder on your network drive (are any files from within the folder open in any other programs which may have put a temporary lock on them?) but as long as saving the new gallery to a new folder works consistently, then this seems to be the way to go.

Juicebox saves the data from the 'Set Image Sizes' pop-up window in preset files and if small or large images are deselected when a preset is saved, then they will also be deselected when the preset is loaded.
I realise that you would rather have Juicebox not save the image size data but this is how Juicebox works and knowing this should at least help you workaround it.

I tried what you described above but was unable to replicate the problem. My test gallery included both small and large images as expected.

Make sure that you click the 'OK' button in the 'Set Image Sizes' pop-up window between changing the sizes and saving the preset.

Also, please make sure that you are using the most recent version of JuiceboxBuilder-Pro (v1.4.3) to ensure that any bugs present in previous versions which have since been fixed are not contributing to your problem. You can check which version you are using by going to 'Help -> About JuiceboxBuilder-Pro' from the drop-down menu at the top.
If necessary, instructions for downloading the current version and upgrading JuiceboxBuilder-Pro can be found on the Upgrading Juicebox support page.

Please check that the images have been uploaded to the correct location on your web server and check that the thumbURL paths in the gallery's XML file point towards the thumbnail images correctly.

You might like to try re-uploading the thumbnail images to your web server in case something happened during the initial upload resulting in missing or corrupt files.

Please also see this FAQ:
My images show locally, but not when I upload them to my website. Why?

Also, check the permissions of the thumbnail files (with a dedicated FTP program such as Filezilla or within your web hosting account's online CPanel) and their parent folders to make sure that they are not too restrictive. Default permissions of 644 for files and 755 for folders should be fine.

If you continue to experience difficulties, then please post back with the URL to your gallery so that I can take a look at the problem for myself and help further.