Since an unknown date, the thumbnail generation for an .tif file on Commons is no longer working. The file:
It was working at least 1.5 years ago when I was editing the file description. The file is still in use in the german article. Currently the usage in enWP has been replaced with its JPG equivalent:
It should be checked if only the file is broken (works with an image viewer under Windows) or if there could be other files affected.