Here is the output of --list-packets of the offending key, anonymised:

1. off=0 ctb=99 tag=6 hlen=3 plen=418 :public key packet: version 4, algo 17, created 985690138, expires 0 pkey[0]: [1024 bits] pkey[1]: [160 bits] pkey[2]: [1024 bits] pkey[3]: [1023 bits] keyid: <KEY_ID>
2. off=421 ctb=b4 tag=13 hlen=2 plen=35 :user ID packet: "XXXXXXXXXXXXX"
3. off=458 ctb=88 tag=2 hlen=2 plen=120 :signature packet: algo 17, keyid <KEY_ID> version 4, created 1629537425, md5len 0, sigclass 0x13 digest algo 2, begin of digest a8 22 hashed subpkt 33 len 21 (issuer fpr v4 <XXXXXXXXXXXXXX><KEY_ID>) hashed subpkt 2 len 4 (sig created 2021-08-21) hashed subpkt 27 len 1 (key flags: 23) hashed subpkt 11 len 4 (pref-sym-algos: 9 8 7 2) hashed subpkt 21 len 5 (pref-hash-algos: 8 9 10 11 2) hashed subpkt 22 len 3 (pref-zip-algos: 2 3 1) hashed subpkt 30 len 1 (features: 01) hashed subpkt 23 len 1 (keyserver preferences: 80) subpkt 16 len 8 (issuer key ID <KEY_ID>) data: [158 bits] data: [159 bits]
4. off=580 ctb=b9 tag=14 hlen=3 plen=525 :public sub key packet: version 4, algo 16, created 985690139, expires 0 pkey[0]: [2048 bits] pkey[1]: [2 bits] pkey[2]: [2046 bits] keyid: YYYYYYYYYYYYYYY
5. off=1108 ctb=88 tag=2 hlen=2 plen=63 :signature packet: algo 17, keyid <KEY_ID> version 3, created 985690139, md5len 5, sigclass 0x18 digest algo 2, begin of digest 94 e5 data: [159 bits] data: [156 bits]