The issue was highlighted by a user reporting a broken panorama view. At the end it turned out, that `thumbs.php` massively cropped the image while resizing it.
See the following examples:
Original: https://commons.wikimedia.org/wiki/File:Stendal-Marktplatz-mit-Rathaus-und-St-Marien-IMG_5262-11x3B-360Gx180G-PanoS-19-05-2023.jpg
w3900: https://commons.wikimedia.org/w/thumb.php?w=3900&f=Stendal-Marktplatz-mit-Rathaus-und-St-Marien-IMG_5262-11x3B-360Gx180G-PanoS-19-05-2023.jpg (fine)
w4000: https://commons.wikimedia.org/w/thumb.php?w=4000&f=Stendal-Marktplatz-mit-Rathaus-und-St-Marien-IMG_5262-11x3B-360Gx180G-PanoS-19-05-2023.jpg (weirdly cropped)
It does not seem to happen with a different version of that image ( that already got a bit cropped ):
Original: https://commons.wikimedia.org/wiki/File:Stendal-Marktplatz-mit-Rathaus-und-St-Marien-IMG_5262-11x3B-eTHI3-GBE-360Gx180G-PanoS-wbk-19-05-2023.jpg
w3900: https://commons.wikimedia.org/w/thumb.php?w=3900&f=Stendal-Marktplatz-mit-Rathaus-und-St-Marien-IMG_5262-11x3B-eTHI3-GBE-360Gx180G-PanoS-wbk-19-05-2023.jpg (fine)
w40000: https://commons.wikimedia.org/w/thumb.php?w=4000&f=Stendal-Marktplatz-mit-Rathaus-und-St-Marien-IMG_5262-11x3B-eTHI3-GBE-360Gx180G-PanoS-wbk-19-05-2023.jpg (fine)
When I import the former version of the file to my local dev wiki and generate a thumb with the same parameters there's no issue. Could currently not upload it to the beta cluster to test it there.
Not sure if related to {T282385}