Both of these are being executed on the same server.
exec xp_logininfo 'Domain\User5', 'all'
Domain\User5useradminDomain\User5Domain\GroupA
exec xp_logininfo 'Domain\GroupA', 'members'
Domain\User1useradminDomain\User1Domain\GroupA
Domain\User2useradminDomain\User2Domain\GroupA
Domain\User3useradminDomain\User3Domain\GroupA
Why is User5 missing from the list of members when User5 is really in Domain\GroupA?