I see a slight variation, but still cannot remove the attribute.

grant@ef-idm01:~[20221123-7:19][#1018]$ ipa user-show --all --raw waynev | grep krblastadminunlock
grant@ef-idm01:~[20221123-7:20][#1019]$ ipa user-show --all --raw waynev | grep -i krblastadminunlock
  krbLastAdminUnlock: 20171006230951Z
grant@ef-idm01:~[20221123-7:20][#1020]$ ipa user-mod --delattr=krbLastAdminUnlock=20171006230951Z waynev
ipa: ERROR: krblastadminunlock does not contain '20171006230951Z'
grant@ef-idm01:~[20221123-7:20][#1021]$

- grant