www.debian.pl has an AAAA (IPv6) record (2a02:c40:1:2::2) but a test request to this address over port 80 did not succeed. Your web server must have at least one working IPv4 or IPv6 address. You should either ensure that validation requests to this domain succeed over IPv6, or remove its AAAA record.
A timeout was experienced while communicating with www.debian.pl/2a02:c40:1:2::2: Get "http://www.debian.pl/.well-known/acme-challenge/letsdebug-test": dial tcp [2a02:c40:1:2::2]:80: i/o timeout
Trace:
@0ms: Making a request to http://www.debian.pl/.well-known/acme-challenge/letsdebug-test (using initial IP 2a02:c40:1:2::2)
@0ms: Dialing 2a02:c40:1:2::2
@10000ms: Experienced error: dial tcp [2a02:c40:1:2::2]:80: i/o timeout