Backup Fails intermittently and Causes DPC Watchdog Error BSOD

We're a small non profit and have an HP Proliant ML350 Gen9 that is running Windows 2016 Server and hosting two VMs also running Win 2016 Server.  For approximately 6 months Windows Server Backup was running a scheduled full backup every morning with no issues.  Following a Windows update the backups started to crash the host with a DPC Watchdog BSOD.  Initially I swapped out one of the two USB Drives I was using for the backup.  Success for a week or so and then the same problem returned. It would crash during the backup (and the backup would fail).  If I swap out drives (or apply updates) it then sometimes works again for a while but then usually starts the crashes again.

I then replaced both USB Drives which again solved the problem temporarily but then it returned.  In analyzing the Dump files as best I am able there does not appear to be any one driver or file that is causing the problem.  It appears to timeout at different times and crash with the dump files indicating different offending modules.  This is an example of two:

Error: DPC_TIMEOUT_TYPE:  SINGLE_DPC_TIMEOUT_EXCEEDED
Crashed: PROCESS_NAME:  System
Caused: 
MODULE_NAME: vmswitch
IMAGE_NAME:  vmswitch.sys

13th Crash:
Error: DPC_TIMEOUT_TYPE:  DPC_QUEUE_EXECUTION_TIMEOUT_EXCEEDED
Crashed: PROCESS_NAME:  svchost.exe
Caused: 
MODULE_NAME: nt
IMAGE_NAME:  ntkrnlmp.exe   

HP insists that it is not a hardware issue with the controller.  I believe I have gone through and updated all relevant drivers.

Recently I adjusted the backup to only include our data files and excluded the Hyper V machines as well as system State and Bare metal.  This backup completed.  

Any suggestions or ideas as to what I could try next?  Is there more information that would help in diagnosing the problem?

Thanks,
Byron