Ok I got ambitious, I reinstalled our primary Starwind Target as Server Core while I had everything down. Now both boxes have replacement Intel Pro 1000 cards installed and still exhibiting the same issue. All within an hour of my backups starting.
I am going to try and lighten the load on this server and see if anything changes. On a positive note, my Full re-syncs for 1TB are now down to less than half a day, before they were almost 2 days, not sure why that changed.
The Latest Gartner® Magic Quadrant™Hyperconverged Infrastructure Software