RRSIG _openpgpkey.debian.org/DS alg 8, id 21715: The TTL of the RRset (28800) exceeds the value of the Original TTL field of the RRSIG RR covering it (3600). See RFC 4035, Sec. 2.2.
_openpgpkey.debian.org/DS has errors; select the "Denial of existence" DNSSEC option to see them.