Try to reset the password on the ADS (for administrator and one of the users you are testing with) and logon from the NAS XSR SMB server again.
Can you add a new user in the ADS (with access rights to the shares) and does this show up on the NAS server. If it does go to that system where the user resides and try to logon.
Check the Account Policies and Kerberos Policy because changing to PDC to ADS now uses Kerberos. Check to see if there is any possible deviation of the FQDN that happened recently with this change. Also was there any changes in Windows to the NAS storage with "\\computer_name" on the share change in the ACL rights in the Windows Server?