[Operators] Unable to federate / tests failing?

[Luke Dashjr]

For a few weeks, my server has been unable to federate with some public 
servers, and running the s2s tests on xmpp.org and check.messaging.one I get 
simply "Error: Connection failed.", but I have no problems connecting to any 
of the DNS resolved IPs from my home machine.

Can anyone inform me what's going on in this case?

My server is dashjr.org (served by zinan.dashjr.org).
My own XMPP address is the same as my email.

Thanks,

Luke