I'm not 100% certain that's the cause, but my testing so far suggests it's probably that. Basically if you have a URL that doesn't point to the original resource, but some copy of it on another instance, it won't resolve. So far I've only tested that on a third instance, but from my experience with the same bug on pleroma, this will occur even if you do it on the resource's origin instance. (fse post referred to from poa.st can't be resolved on fse.) As example: https://lemmy.perthchat.org/api/v3/resolve_object?q=https://lemmy.ml/post/472799. It's possible that this is actually just a federation block, but https://beehaw.org/post/125367/comment/32382 also fails, (and fetching that post works,) which I'm pretty sure isn't.