Linked Contacts don't stay linked
I have MacOS 14.6.1 set up with both an iCloud and a Google account. I have Contacts set to use both of them. I see both accounts have Contacts in them.
Sometimes I see that both accounts have a card for the same person. I select them both and link them. It all looks fine (there is just one card in Contacts). Sometime later I come back and both cards are back. I haven't edited them — I think it is because of a background sync.
One other thing I'll note is that the Look for Duplicates doesn't find these for some reason. Which is surprising because in some cases they are very similar or seemingly identical.