Account deleted. IIRC the instance disappeared for a while (mastodon.social in this case) then I couldn't login anymore. Other instances (e.g., mastodon.uno) of course don't keep my whole message history. At first I understood that communities are shared, you can post in the same community from many account (often the example of "email is federated" is used). But I'm not sure anymore. Seems the case for c/announcements, but not for many others, so you have communities which are are already little further fragmented.

The federated paradigm and its fragmented nature has differences we need to get used to.