The easiest solution, @
Ophenia, would be just to have Saurfang be lying. It solves a whole lot of plot holes immediately - Saurfang didn't magically track invisible sleepless rogues, but rather he was the one tracked and was aware of it, hence going to Thrall to show him that the Horde is now zombies trying to off him. We know Saurfang can lie. He lied to Memeboi about everything in Old Soldier as his true plan was to commit suicide so that Anduin could defeat the Horde after all, and his whole plan in A Good War was based heavily on deception. Now he'd be making a white lie to get what he sees as the representation of 'his' Horde back on his side.
This won't happen, of course, but it's the easiest fix.