Hi,
Which cDOT version is it?
Have you tried this KB, it has number of steps for troubleshooting CIFS access issue, may be worth going through it once.
https://kb.netapp.com/app/answers/answer_view/a_id/1071815
https://kb.netapp.com/app/answers/answer_view/a_id/1070767
Some basic standard questions:
1) Ensure AD & Filer time is within 5mnt.
2) Do you have host A record for netapp cifs-server in the DNS
3) Don't know whow many DCs you have? But in the pic, looks like one : 172.23.4.2
Testing : Could you go to that server and disable netbios on DC? Netbios in general takes more than 2 seconds to reply, that could be the reason for DCs not responding in time to storage.
Thanks!