I just upgraded to 12 U3.1 and had the same /similar issue.
when I checked after the upgrade none of my shares where active:
# smbclient -L ip
Sharename Type Comment
--------- ---- -------
IPC$ IPC IPC Service (FreeNAS Server)
When I disabled and enabled the shares they became active. But I still can't login.
in /var/log/samba4/auth_audit.log I get:
{"timestamp": "2021-05-13T21:37:55.738302+0200", "type": "Authentication", "Authentication": {"version": {"major": 1, "minor": 2}, "eventId": 4625, "logonId": "0", "logonType": 3, "status": "NT_STATUS_NO_SUCH_USER", "localAddress": "ipv4:ip:445", "remoteAddress": "ipv4:ip:56856", "serviceDescription": "SMB2", "authDescription": null, "clientDomain": "WORKGROUP", "clientAccount": "ig", "workstation": "x", "becameAccount": null, "becameDomain": null, "becameSid": null, "mappedAccount": "ig", "mappedDomain": "GALAXY", "netlogonComputer": null, "netlogonTrustAccount": null, "netlogonNegotiateFlags": "0x00000000", "netlogonSecureChannelType": 0, "netlogonTrustAccountSid": null, "passwordType": "NTLMv2", "duration": 1720}}
As I found these posts I created a Debug file.
But then I rolled back. It would be annoying to reinstall the system ... :-/