Sometimes, group members may not be visible when running the getent group groupname command. This can be caused by an incorrect ldap_schema in the [domain/DOINNAME] section of the sssd.conf file. SSSD supports three LDAP schema types: RFC 2307, RFC 2307bis, and IPA. By default, SSSD uses the more common RFC 2307 schema. The difference between RFC 2307 and RFC 2307bis is the way which group membership is stored in the LDAP server. In an RFC 2307 server, group members are stored as the multi-valued memberuid attribute which contains the name of the users that are members. In an RFC2307bis server, group members are stored as the multi-valued attribute member (or sometimes uniqueMember) which contains the DN of the user or group that is a member of this group. RFC2307bis allows nested groups to be maintained as well.
When encountering this problem:
add ldap_schema = rfc2307bis in the sssd.conf file,
detele the /var/lib/sss/db/cache_DOMAINNAME.ldb file,
and restart SSSD.
If the workaround does not work, add ldap_group_member = uniqueMember in the sssd.conf file, delete the cache file and restart SSSD.