I seem to recall from reading a GitHub issue that a public cert and private key is generated for your user account upon creation. Once you start federating and interacting with other instances, the cert is distributed. When you delete the instance and start all over from scratch with the same username, now there’s a different public cert and the remote instances no longer trust your username.
I’ll try to find the GitHub issue that discusses this issue.
I’m starting to think Microsoft’s marketing department gets incredibly bored lol. Like the time they renamed Lync to Skype for Business.