You have two name servers but only one of them returns an A record. Let's Encrypt needs all of them to return the correct reply as it may query any of them.
Check your ns2 server. You can reproduce by repeatedly running https://unboundtest.com query for your A record
From my own machine I get no reply from ns2
dig +noall +answer searx.pl4.fi @ns2.dy.fi
dig +noall +answer searx.pl4.fi @ns1.dy.fi
searx.pl4.fi. 30 IN A 95.217.73.32