Moodle newbie here, please let me know if I'm in the right spot to report this issue or if I need to go somewhere else.

When upgrading to version 3.3, there seems to be a issue with generating thumbnails for audio and video media. It seems like image media will correctly generate thumbnails since it has image media to fall back on.

 See 1.png attached

Any Gallery that contains any media other than a image will break the thumbnail images.

I believe this may be a Moodle issue and not a plug-in issue because of certain files that have changed when updating to version 3.3

Inside of lib/filelib.php the way that $fileicons are generated has changed. 

 See 2.png attached

You can see above how thumbnail files were originally referencing png files, but now they are referencing SVG files. When I look at the directory where these images are being stored, I can see they are still being stored as png images, and not SVG images.

Another possible cause is the actual thumbnail upload section. 

 See 3.png attached

You can see the "Use as a Thumbnail" section. This always will revert to "No" regardless of the media type. The thumbnail upload section also clears out all files.

Please let me know if you need any additional information about this. I appreciate the communities help.

Thanks