Issue: images missing

I suspect that at the time these files were uploaded, your server did not have PNG support compiled in PHP. This means that VaultWiki was unable to determine the image dimensions and set them as 0 width and 0 height at the time you uploaded the image.

This did not make a difference until 4.0.15, when we started using the known dimensions in order to display the images. Since the known dimensions are 0 x 0, the images are too small to see.

Please check if PHP now has PNG image support. If you can't find this information, try editing PNG in Admin Panel > Content > Attachments. Make a small change such as reducing the maximum allowed width by 1 pixel, and save. Then edit it again. If "Yes" is still chosen for "Is this an image type?" at this time, then you currently have PNG support. If you still do not have PNG support, then you should recompile PHP with it, and change this back to "Yes". Once PNG support is confirmed, please submit a ticket, because we will need to develop a custom solution for this special case:

An image was uploaded while the server did not support the uploaded image type, but support is added later. In this case, a special tool will need to reprocess the affected images.

If PNG support is not added, then the fact that the image works as an image at all is a bug. The correct behavior would be to treat the file as downloadable, with a link to do so. For this, I believe this bug might apply to attachment-types that were created prior to 4.0.5, or that had "Is this an image type?" manually set to "Yes" (while there was no server support) prior to 4.0.8.

these images were displayed before the update.... :-(

I can't find Admin Panel > Content > Attachments on Xenforo...

While the bugs I mentioned above did affect some images on your site, the issue you were experiencing in the posted example was actually a special case when the FILE BB-Code used the link= parameter. In this case, the final dimensions were not being applied to the image, which caused them to render too small to see.

The case with the link= parameter is now fixed on your site and will be fixed in the next build of 4.0.15.
I am still working on a solution for the bugs above involving changes to the server's built-in image support.

Fixed in the next release. The wiki will continuously check that the image types supported by GD and Imagick have not changed since the last cache was built. If they have, the cache for attachment types is invalidated, and any image types that are no longer support are automatically treated as non-image types.