Some of those interactions will simply need time to propagate. However, there's a number of things going on here. Aside from the fact that the federation process itself probably needs some tuning/optimization for the current number of users, before 0.18 one of the goto workarounds for hot/active being broken were regular restarts. Everytime they restarted anything in the outbound queue was lost. I believe they would still show locally though. All that said I think this is primarily a case of slow propogation. Particularly because of the migration wave.