The only thing that bothers me about Mastodon so far, and it's relatively minimal, is that there's a lot of names that are familiar to me from Twitter, but I don't follow them on Twitter... and I can't remember why it is the case. Did I unfollow them at some point ? Why ? What did you do ??? XD
For instance at some point in time I started unfollowing people with stealthy TERF attitude. Like, they'd quietly RT a subtle tweet here and there but would mostly not mention it... and a lot of them I set aside quietly. But now, how do I remember who's who ?! :P
So, you see, relatively small problems.