It might be related to this:
https://kbin.social/m/random/t/134102/Blocking-instances-to-clear-the-500k-queue#comments

Today kbin.social is blocking a huge list of domains just to get federation working again.

The reason for this temporally block is not to defederate, but rather to get the large backlog of 500k messenger queue processed again. Anyway, this does mean that kbin.social is federating again with other instances.

This is a temporary measure. Several users / developers are looking into how to better optimize the failed message queue, as we speak. Hopefully Ernest has eventually time to dive into solutions as well instead of workarounds, once his instance is migrated to Kubernets. See my preview thread: https://kbin.melroy.org/m/updates/t/4257/Kbin-federation-issues-and-infra-upgrade