Lemmy isn’t even at a point 2 minor version yet so it will be awhile before it is stable and these kind of kinks worked out, but this kind of thing is going to somewhat the norm I think, by design.

Beehaw defederated Lemmy.world, and they are both have large communities. Although we federate with them both, depending on who/where it was posted the source of truth may result in not always getting consistent updates from both.

I believe the reality in federated space is you will always want to have an account on all the more active instances, using one local as your primary and monitoring things you want to follow on multiple. Luckily the official app makes it pretty easy to do, and maybe there is another app, or one in the works, that will do a client side merge across accounts.