I have enabled debugging in pam_winbind.conf but strange things happen... this is what I've done:

root@103note0512:~# smbcontrol winbind offline
root@103note0512:~# smbcontrol winbind onlinestatus
PID 1102: global:Offline BUILTIN:Online 103NOTE0512:Online MYDOMAIN:Offline 
root@103note0512:~# ssh MYDOMAIN\\myuser@localhost
MYDOMAIN\myuser@localhost's password: 
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-45-generic x86_64)
[...]
Last login: Tue Feb 12 14:45:36 2019 from 127.0.0.1
MYDOMAIN\myuser@103note0512:~$ 

and all seems to works but if I exit and I disconnect the PC from the local network and try again I can't connect:
root@103note0512:~# ssh MYDOMAIN\\myuser@localhost
MYDOMAIN\myuser@localhost's password: 
Permission denied, please try again.

In /var/log/auth.log I can find the following debug info:
Feb 12 14:55:12 103note0512 sshd[4228]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=127.0.0.1  user=MYDOMAIN\myuser
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] ENTER: pam_sm_authenticate (flags: 0x0001)
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_SERVICE) = "sshd" (0x56235e259740)
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_USER) = "MYDOMAIN\myuser" (0x56235e25a8e0)
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_TTY) = "ssh" (0x56235e269900)
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_RHOST) = "127.0.0.1" (0x56235e2698e0)
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_AUTHTOK) = 0x56235e269cb0
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_CONV) = 0x56235e269a50
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): getting password (0x00001389)
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): pam_get_item returned a password
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): Verify user 'MYDOMAIN\myuser'
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): PAM config: krb5_ccache_type 'FILE'
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): enabling krb5 login flag
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): enabling cached login flag
Feb 12 14:55:12 103note0512 sshd[4228]: pam_winbind(sshd:auth): enabling request for a FILE krb5 ccache
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): request wbcLogonUser failed: WBC_ERR_AUTH_ERROR, PAM error: PAM_SYSTEM_ERR (4), NTSTATUS: NT_STATUS_INVALID_PARAMETER, Error message was: An invalid parameter was passed to a service or function.
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): internal module error (retval = PAM_SYSTEM_ERR(4), user = 'MYDOMAIN\myuser')
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] LEAVE: pam_sm_authenticate returning 4 (PAM_SYSTEM_ERR)
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_SERVICE) = "sshd" (0x56235e259740)
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_USER) = "MYDOMAIN\myuser" (0x56235e25a8e0)
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_TTY) = "ssh" (0x56235e269900)
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_RHOST) = "127.0.0.1" (0x56235e2698e0)
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_AUTHTOK) = 0x56235e269cb0
Feb 12 14:55:33 103note0512 sshd[4228]: pam_winbind(sshd:auth): [pamh: 0x56235e25be70] STATE: ITEM(PAM_CONV) = 0x56235e269a50
Feb 12 14:55:36 103note0512 sshd[4228]: Failed password for MYDOMAIN\\myuser from 127.0.0.1 port 35868 ssh2
 
I am very confused...

Piviul