Avamar Timeout for some VMs

Greetings,

We're having an issue where 3 of our 20 something VMs fail to backup because they timeout every day in the last week.

In viewing the logs on the VMware host, all of the VMs that have a functional Avamar backup also show that the backup user logs in, performs a snapshot, and then deletes it after the back up is complete. The 3 VMs that do not work have no indication of a snapshot being requested and the backup operation times after 4 hours. We've tried to run the backup manually from Avamar but the Avamar activity logs says "Waiting for client" and the VMware host logs show no indication that the backup user has logged in to perform a snapshot. Normally it occurs within ~2 minutes of the requested backup time. All 3 of the non-working backup VMs started having issues on the same day. No one has changed any settings in Avamar or the VMware host. I tried removed one of the VMs from the Avamar backup policy and re-added it but it had no effect. The backup user in VMware is applied to the host and its children so it shouldn't have any issue being used by those 3 VMs. We have rebooted the VMs as a straw-grasping maneuver. We don't seem to have a storage space issue, either.

Anything in particular I should be looking at? 

Thanks.