Anyone else notice that upvotes from members of some of the instances appear as downvotes to people in certain other instances?

What on earth are you talking about? This almost certainly doesn't happen. The person who guessed that it was a misclick followed by a not-yet-federated correction, might be onto something, but my feeling is that it's some more basic misunderstanding than that.

If you DM me the example you're seeing I can probably dig into the details and tell you what's going on.

Maybe a misclick where correction after it didn't federate? Dunno.

nope. got examples?

Yeah, I've never seen that happen either. We'd need some links and screenshots to help.

You must be talking about instances that have disabled downvotes.