It is not a bug as it is blocking the specific user agent, it blocks all requests with that user agent even for things that cannot cause any incompatibility (like just querying user info from the command line). Also no other lemmy instance shows this 'bug', regardless of version. It is a very deliberate block either done manually or by an IDS.

Would be nice if a server admin would chime in, but it is very silent on all channels.

Is kbin commonly open to federate with?

I tried to subscribe to some magazines from my own private lemmy instance, no errors are thrown in the log, but there is no activity following up. The subscription stays pending and no posts show up.

My guess would be that kbin.social is only talking with some bigger lemmy instances?