76F summer 74F winter

I’m new to it all so I registered on lemmy.world and subscribed to several communities. I also registered and subscribed to the same communities on lemmy.ee. When lemmy.world is down, I use lemmy.ee, but those subscribed communities that are local on lemmy.world are no longer accessible. I thought communities synced over instances so if an instance goes down, communities are still accessable. Is this not true?