Lately we have been dealing with a few abusive members from Feddit.nl and we were unable to get in touch with the instance administrator.
Part of the problem is the instance’s open registrations which do not require you to enter an e-mail address during signup. This in combination with an inactive admin is a recipe for abuse.
We hope this is only temporary but we have to do this to protect our users.
Edit: we use fediseer, have a look https://gui.fediseer.com/instances/detail/lemmy.world
Edit 2: We got in touch with the Feddit.nl admin. Email requirements were added to the sign-up process and we’re setting up a communication channel. So that means we are federating with Feddit.nl again!
Just to play devil’s advocate; it seems like maybe an instance with a very active mod team would be another criterion to add to your list.