Error renewing certificate from LE (not Docker)

Up to now renewing certificates worked without problem. But the currently I get:

... error: one or more domains had a problem:\n[] acme: error: 400 :: urn:ietf:params:acme:error:connection :: 
Timeout during connect (likely firewall problem)\n" providerName=letsencrypt.acme

Maybe this is the result of adding country blocking rules.

So my question is: Who i.e. what server (name,IP) tries to fetch the challenge or where is it located?