Hi,
I have a ClearOS 7.8 system which is running 
samba-4.10.4-11.el7_8.x86_64, and it upgraded to this just over a week 
ago (probably not relevant). A couple of days ago all the group shares 
failed. I discovered that if I switched them to the built-in group 
"allusers" the share worked fine. It fails for any user-defined group 
but it used to work. Samba is running as a PDC and the configs, 
including one share are:
    [root at server ~]# testparm -s
    Load smb config files from /etc/samba/smb.conf
    NOTE: Service profiles is flagged unavailable.
    Loaded services file OK.
    'winbind separator = +' might cause problems with group membership.
    Server role: ROLE_DOMAIN_PDC
    # Global parameters
    [global]
     ??????? add machine script = /usr/sbin/samba-add-machine "%u"
     ??????? domain logons = Yes
     ??????? domain master = Yes
     ??????? guest account = guest
     ??????? interfaces = lo enp8s0f0
     ??????? ldap admin dn = cn=manager,ou=Internal,dc=sha,dc=lan
     ??????? ldap connection timeout = 8
     ??????? ldap group suffix = ou=Groups,ou=Accounts
     ??????? ldap idmap suffix = ou=Idmap
     ??????? ldap machine suffix = ou=Computers,ou=Accounts
     ??????? ldap ssl = no
     ??????? ldap suffix = dc=sha,dc=lan
     ??????? ldap user suffix = ou=Users,ou=Accounts
     ??????? log file = /var/log/samba/%L-%m
     ??????? logon drive = H:
     ??????? logon home = \\%L\%U
     ??????? logon path      ??????? logon script = logon.cmd
     ??????? max log size = 0
     ??????? ntlm auth = ntlmv1-permitted
     ??????? passdb backend = ldapsam:ldap://127.0.0.1
     ??????? passwd chat = *password:* %n\n *password:* %n\n *successfully.*
     ??????? passwd chat timeout = 10
     ??????? passwd program = /usr/sbin/userpasswd %u
     ??????? preferred master = Yes
     ??????? printcap name = /etc/printcap
     ??????? security = USER
     ??????? server string = ClearOS Server
     ??????? template homedir = /home/%U
     ??????? template shell = /sbin/nologin
     ??????? unix password sync = Yes
     ??????? username map = /etc/samba/smbusers
     ??????? utmp = Yes
     ??????? winbind enum groups = Yes
     ??????? winbind enum users = Yes
     ??????? winbind expand groups = 1
     ??????? winbind separator = +
     ??????? winbind use default domain = Yes
     ??????? wins support = Yes
     ??????? workgroup = SHA
     ??????? idmap config * : ldap_user_dn    
cn=manager,ou=Internal,dc=sha,dc=lan
     ??????? idmap config * : ldap_base_dn = ou=Idmap,dc=sha,dc=lan
     ??????? idmap config * : ldap_url = ldap://127.0.0.1
     ??????? idmap config * : range = 20000000-29999999
     ??????? idmap config * : backend = ldap
     ??????? include = /etc/samba/flexshare.conf
    [test]
     ??????? comment = test
     ??????? create mask = 0664
     ??????? directory mask = 0775
     ??????? path = /var/flexshare/shares/test
     ??????? read only = No
     ??????? valid users = @%D\admin @admin
     ??????? veto files = /.flexshare*/
If I try using smbclient I get:
    [root at server shares]# smbclient //localhost/test -c 'ls' -U
clearcenter
    Enter SHA\clearcenter's password:
    tree connect failed: NT_STATUS_ACCESS_DENIED
If I change the valid users to the "allusers" group and change the 
folder permissions, it works fine.
I get:
    [root at server ~]# wbinfo --group-info='staff'
    failed to call wbcGetgrnam: WBC_ERR_DOMAIN_NOT_FOUND
    Could not get info for group staff
    [root at server ~]# wbinfo --group-info='allusers'
   
allusers:x:63000:flexshare,clearcenter,zschladen,fferri,myantzi,echarron,kjohnson,printer,debacker,mmcleod,dseydoux,shiggins,email-archive,guest
    [root at server shares]# net groupmap list
    allusers (S-1-5-21-1661951805-1908507638-2940817366-63000) -> allusers
    Guests (S-1-5-32-546) -> guests
    dropbox_plugin (S-1-5-21-1661951805-1908507638-2940817366-60000) ->
    dropbox_plugin
    imap_plugin (S-1-5-21-1661951805-1908507638-2940817366-60001) ->
    imap_plugin
    openvpn_plugin (S-1-5-21-1661951805-1908507638-2940817366-60002) ->
    openvpn_plugin
    print_server_plugin
    (S-1-5-21-1661951805-1908507638-2940817366-60003) -> print_server_plugin
    smtp_plugin (S-1-5-21-1661951805-1908507638-2940817366-60004) ->
    smtp_plugin
    user_certificates_plugin
    (S-1-5-21-1661951805-1908507638-2940817366-60005) ->
    user_certificates_plugin
    Domain Admins (S-1-5-21-1661951805-1908507638-2940817366-512) ->
    domain_admins
    Domain Users (S-1-5-21-1661951805-1908507638-2940817366-513) ->
    domain_users
    Domain Guests (S-1-5-21-1661951805-1908507638-2940817366-514) ->
    domain_guests
    Domain Computers (S-1-5-21-1661951805-1908507638-2940817366-515) ->
    domain_computers
    Administrators (S-1-5-32-544) -> administrators
    Users (S-1-5-32-545) -> users
    Power Users (S-1-5-32-547) -> power_users
    Account Operators (S-1-5-32-548) -> account_operators
    Server Operators (S-1-5-32-549) -> server_operators
    Print Operators (S-1-5-32-550) -> print_operators
    Backup Operators (S-1-5-32-551) -> backup_operators
    executive (S-1-5-21-1661951805-1908507638-2940817366-60006) -> executive
    staff (S-1-5-21-1661951805-1908507638-2940817366-60007) -> staff
    visitors (S-1-5-21-1661951805-1908507638-2940817366-60008) -> visitors
    admin (S-1-5-21-1661951805-1908507638-2940817366-60009) -> admin
One of the Samba logs goes:
    [2020/07/16 05:29:48.583319,? 1]
    ../../source3/smbd/service.c:359(create_connection_session_info)
     ? create_connection_session_info: user 'clearcenter' (from session
    setup) not permitted to access this share (test)
I notice the messages log gives:
    Jul 16 04:34:28 server winbindd[21471]: [2020/07/16
    04:34:28.069299,? 0]
    ../../source3/winbindd/idmap_ldap.c:85(get_credentials)
    Jul 16 04:34:28 server winbindd[21471]:? get_credentials: Unable to
    fetch auth credentials for cn=manager,ou=Internal,dc=sha,dc=lan in *
I have tried clearing the winbindd_cache.tdb and gencache.tdb but am 
wary of clearing anything else without instruction.
Please can you help me?
Thanks,
Nick