After I uploaded https://wikitech.wikimedia.org/wiki/File:Dbbackups_dashboard_status.png the file was not shown (and it doesn't appear to be a thumb issue because it says the file doesn't exist). This happens consistently, also happened at: https://wikitech.wikimedia.org/wiki/File:Screenshot_20230411_155237.png
Edit: The file is physically accessible by direct url, but it is not shown or linked to.
Additional note:
It correctly lists those files (but without thumbnails in the former) at both
https://wikitech.wikimedia.org/wiki/Special:ListFiles and
https://wikitech.wikimedia.org/wiki/Special:Log/upload
Nice, I see then that the file is there, will correct the title. I don't know now then if there is a metadata issue or "a file doesn't exist" is what it returns automatically when there is no thumb.
Adding @Andrew, mostly for awareness, and in the small chance he knows of any system-level change that could have caused that (even if unlikely).
I experienced the same last week at https://wikitech.wikimedia.org/wiki/File:WikimediaDebug_v2.7_output-links.png. I ended up working around it by uploading to Commons instead.
It seems though that a few days later, the file has now appeared!
So maybe it is just the usual thumbnail issue? I can merge tasks, if a missing thumbnail would cause mw to say "File not found".