There could be lots of reasons. the three i have in mind from your description:
1. is there full connectivity from the filer to all DC's on the other domain?
2. are the clock of the two domains synced from a proper adjusted NTP and so as the filer? (timezone is not relevant. the required sync is on UTC+0)
3. as its old ontap and "new" domain. if the new domain is harden or updated with some patches. is it still support SMB1 (the filer must have options cifs.smb2.client.enable set if not), does it support netbios? (if not options cifs.netbios_over_tcp.enable need to be disabled).
there could be lots more reasons. you will need to troubleshoot further to find your cause, there's a full guide here: