The problem with your '2018nordart' gallery is with the images on your web server.

According to your gallery's 'config.xml' file (https://www.haselau.eu/jb/2018nordart/config.xml), the first image in your gallery should be located here: https://www.haselau.eu/jb/2018nordart/i … 202018.jpg
However, going directly to the image's URL in a web browser (bypassing Juicebox) displays a blank page instead of the image.
Going directly to the image's URL in a web browser should display the image (completely independent of Juicebox) but this does not happen so the problem is with the image on your web server rather than with Juicebox itself.

First of all, please double-check that the images have been successfully uploaded to your web server.
It looks like the blank page may actually be an error 404 (file not found) page so the images may not have been uploaded to the correct location on your web server.

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

If this does not help, then the problem could be due to your image filenames containing special characters (such as "ü").

As an image filename forms part of a URL when uploaded to a web server, it would be wise to use only web-safe characters within image filenames. Please see section 2.3 of this document for details.

You should have no trouble (either in JuiceboxBuilder-Pro or on your web server) if your image filenames use only these web-safe characters.

With this in mind, try renaming your images to use only web-safe characters within their filenames to see if this helps.

I'm glad that you have been able to resolve your problem but, just to clarify, the problem is with your web server rather than with Juicebox itself.

Essentially, you uploaded an image to your web server with an accented character in its filename and your web server was unable to display it when you went directly to its URL.
(The image happened to be inside a Juicebox gallery folder but this test actually has nothing to do with Juicebox.)
If the browser is unable to display the image directly, then Juicebox will also be unable to display the image in the gallery.

I would always recommend using only web-safe characters for image filenames but, just to let you see that Juicebox can handle accented characters in image filenames, here's a single-image test gallery (created by JuiceboxBuilder-Pro) where the image in the gallery is named "éèâîôñüïç.JPG": [Link deteled.]

As long as the web server is happy with accented characters, then Juicebox will be, too.

Try contacting your web host to see if they have made any changes recently which might be affecting your results.

I cannot be sure of the exact reason why your gallery did not load your images (which is why I gave a few different suggestions).
All I can say with any certainty is that when I went to view one of your images directly (bypassing Juicebox), your web server did not display it and when I viewed the source of the 'blank' page in my browser, I saw HTML code which looked like a generic error 404 page.
The HTML code I saw (the source of the 'blank' page on which the image should have been displayed) was exactly the same HTML code that I see when I view the source of any web page on your web site that definitely does not exist, such as: https://www.haselau.eu/this_web_page_do … exist.html
This suggested to me that the images had not been uploaded to the correct location on your web server (and this is why my first suggestion was to check that the images had been uploaded to your web server successfully).

Juicebox can display images which contain accented characters as long as your web server can (my test gallery demonstrates this) so try again with your accented filenames if you like (although I'd still recommend using only web-safe characters for image filenames and leave accented characters for image titles and captions).

However, please note that JuiceboxBuilder-Pro does not accept images which contain #, ? and ' characters.
This is noted in the Known Issues section of the JuiceboxBuilder-Pro User Guide.
These characters are reserved characters in URLs (rather than just being accented characters) and ideally should not be used within image filenames.