I had the same issue.
here's how I fixed it:
Restart the Unraid,
dont initialize the array just yet....
go to SETTINGS, Network Settings, change the desired MTU: to 1500( you have to put in 1500, what shows in the box is just a place-holder and not the actual number 1500)
Click on APPLY.
you will lose network connectivity, so go to the server and restart it there.