VNX 5800 CIFS shares unavailable

We began having an issue shortly after a code upgrade to File Software version 8.1.9-217, we had to delay the data mover reboot until an early morning downtime window on a weekend. 10 days later on a Wednesday between 11:30-11:45 the CIFS data becomes unavailable for 10 - 12 minutes. This was in May, it has occurred each week at the same time since then, we do not have any scheduled activities and all other units deny any type of scan or other activity. Throughput on the switch goes from an average over 300Mbps dropping to less than 10Mbps then ramps back up.

We initially found that the 10G ports had been connected to a FEX and we moved those to the 5K switches, no change in behavior.

Failed over/failed back DM

Removed device from port group on Server_2 during the issue no change.

Logs show nothing conclusive, support says traces show frame delivery issues and high amount of smb2 create and close which may indicate application scanning operation

Running out of possible scenarios to check, any suggestions?