I know the text you are getting. I have had that on Asus Crosshair VI Hero. Occurs when a EC FW has been updated due to a newer UEFI flashed to board. It will happen one time on first post after flash and then not.
Viewing your screenshot we have the same EC FW for all on board. So you shouldn't be repeatedly getting the message of update.
If in your shoes I would remove power fully from rig, do clear CMOS, then switch on wall plug and using 'Flashback' method flash 0601. After you have had a successful post shutdown again, remove power from rig, do clear CMOS. Boot up and see if all is fine.
I agree tech support can be clueless at times on issues like this.