See AdguardTeam/AdGuardHome#5557. Client.DialStamp uses Client.fetchCert, which has bad error handling. certErr is overwritten on every iteration of the loop over r.Answer and is never set at all if there are no answers or if none of the answers are TXT. That results in Client.fetchCert returning nil, nil, which leads to a panic in Client.DialStamp.

Client.fetchCert has a cyclomatic complexity of 14 and a cognitive complexity of 23 and needs refactoring.