What you’re experiencing (in terms of user management interface) is not a direct bug, but a currently a normal behavior of Zammad. (see: https://github.com/zammad/zammad/issues/2214)
Note that depending on your LDAP server you may experience limits in term sof number of objects your LDAP server provides before closing the connection. But let’s not mix things up.
I’ve ended up side stepping the issue by not using LDAP or local login and just using Google login and SAML. Users are only generated on first login so the issue with the bulk creation seems to have been avoided.
I’m not 100% sure this isn’t a different issue though, because I couldn’t even search for other users when I was using LDAP. But again I’ve side stepped this by just using SAML and Google Logins for my users.