Its reproducible  in both RHEL8 and RHEL9

SSSD version being tested: sssd-2.9.1-2

[root@client1 ~]# getent passwd usr_2
usr_2:*:345832:345832:usr_2 User::/bin/bash
[root@client1 ~]# getent group ldapgrp
ldapgrp:*:345641:usr_1,usr_2,usr_3

> Delete the user.
(Pdb)         user_dn = 'uid=usr_2,ou=People,dc=example,dc=test'
(Pdb)         ldap_inst.del_dn(user_dn)
('Success', (107, [], 8, []))
(Pdb)

[root@client1 ~]# sss_cache -E
[root@client1 ~]# getent group ldapgrp
ldapgrp:*:345641:usr_2,usr_1,usr_3
[root@client1 ~]# getent passwd usr_2
[root@client1 ~]# getent group ldapgrp
ldapgrp:*:345641:usr_1,usr_2,usr_3