Ok the next thing support had me test is to re-enable parallel processing, but on one job choose a specific Veeam proxy. Then in the backup infrastructure on that veeam proxy specify the network transport mode.
So I did that as a test and last night this job completed sucessfully (about 45 minutes FASTER than usual too).
This got me thinking... We are an NFS shop here, why not try the new direct storage access? Both of my Veeam proxies have a second nic on that storage network and can ping our EMC VNX5200 NFS interfaces. So I went into our EMC VNX5200 storage array configuration and gave both Veeam proxies IP addresses as full access to our NFS file systems. I am testing a job right now and its sucessfully backedup 11 VM's in 15 minutes 17 seconds. Now the backup already ran a few hours ago so there was only 12.8 GB of changed data out of the 745.9 GB processed and 28.5 GB read.
Tonight I will be excited to see how NFS direct access handles the jobs, and also correlate if our alert-bot text message does not go out about our website not being accessible. See with NFS and hotadd, if a machine is not on the same ESXi host as the Veeam proxy (and it won't always be since we have 2 proxies but 6 hosts), when the hotadd disk is released it stuns the VM and it looses pings / nework connectivity. So I'm hoping that this mode will help according to https://www.veeam.com/kb1681
I know that is deriving a little off topic, however maybe you can try the different transport modes. For me network worked, and nfs appeared to work as well on one job I tested it with.