This is whats appearing in the log:
root@freenas[~]# tail /var/log/samba4/log.smbd
{"timestamp": "2019-06-03T20:32:13.237396-0700", "type": "Authentication", "Authentication": {"version": {"major": 1, "minor": 0}, "status": "NT_STATUS_WRONG_PASSWORD", "localAddress": "ipv4:192.168.100.21:445", "remoteAddress": "ipv4:192.168.100.7:52539", "serviceDescription": "SMB2", "authDescription": null, "clientDomain": "CLEANED", "clientAccount": "backup", "workstation": "DNS", "becameAccount": null, "becameDomain": null, "becameSid": null, "mappedAccount": "backup", "mappedDomain": "CLEANED", "netlogonComputer": null, "netlogonTrustAccount": null, "netlogonNegotiateFlags": "0x00000000", "netlogonSecureChannelType": 0, "netlogonTrustAccountSid": null, "passwordType": "NTLMv1", "duration": 5517}}
[2019/06/03 20:32:13.963595, 2] ../source3/param/loadparm.c:2815(lp_do_section)
Processing section "[Backup]"
[2019/06/03 20:32:13.965085, 2] ../libcli/auth/ntlm_check.c:430(ntlm_password_check)
ntlm_password_check: NTLMv1 passwords NOT PERMITTED for user backup
[2019/06/03 20:32:13.965775, 2] ../source3/auth/auth.c:334(auth_check_ntlm_password)
check_ntlm_password: Authentication for user [backup] -> [backup] FAILED with error NT_STATUS_WRONG_PASSWORD, authoritative=1
[2019/06/03 20:32:13.965865, 2] ../auth/auth_log.c:610(log_authentication_event_human_readable)
Auth: [SMB2,(null)] user [CLEANED]\[backup] at [Mon, 03 Jun 2019 20:32:13.965845 PDT] with [NTLMv1] status [NT_STATUS_WRONG_PASSWORD] workstation [DNS] remote host [ipv4:192.168.100.7:52541] mapped to [CLEANED]\[backup]. local host [ipv4:192.168.100.21:445]
{"timestamp": "2019-06-03T20:32:13.966222-0700", "type": "Authentication", "Authentication": {"version": {"major": 1, "minor": 0}, "status": "NT_STATUS_WRONG_PASSWORD", "localAddress": "ipv4:192.168.100.21:445", "remoteAddress": "ipv4:192.168.100.7:52541", "serviceDescription": "SMB2", "authDescription": null, "clientDomain": "CLEANED", "clientAccount": "backup", "workstation": "DNS", "becameAccount": null, "becameDomain": null, "becameSid": null, "mappedAccount": "backup", "mappedDomain": "CLEANED", "netlogonComputer": null, "netlogonTrustAccount": null, "netlogonNegotiateFlags": "0x00000000", "netlogonSecureChannelType": 0, "netlogonTrustAccountSid": null, "passwordType": "NTLMv1", "duration": 5625}}