>>1551
So I avoided using the dupe filter altogether during all this time to make sure it has nothing to do with it and while the frequency of these weird dupes reduced, they continue to appear. Either way, I never encounter them in the filter before they show up here and I always delete the dupes I find.
These weird dupes differ only in compression as they usually involve an image imported (from API) a long time ago and its copy retrieved recently, probably because the server's compression format being updated. They have multiple image urls, some are matching, others different between the two.

So basically these are images that got assigned the same dupe group without going through the filter where I would have deleted one. Instead I have to look for these stealth dupes in a special search query.