You know how some subreddits would ban you if you posted in another one? That's basically all this is. We're on lemmy.world which is less guarded, so we're lumped in with troublemakers.
Just like with reddit, the solution is to make a new account without affiliation to the defederated groups. There's a bajillion smaller lemmys out there that will likely never get defederated, and it makes the most sense to have one of those be your home vs the largest instances, now that we can see this kind of problem will occur.