Had this happen to two locomotives in a row within about 20 minutes of each other.
A loco that had previously operated just fine came up as ENOT when I tried to boot it up. I checked and double checked everything I could think of and finally (figuring I had nothing to lose) told DCS to add an MTH engine. Sure enough, DCS found the engine and assigned it to a new address. Now the engine is in the system twice but with different #'s.
Moments later, the exact same scenario played out with another engine.
I deleted the earlier engine(s) from the list and everything seems to be okay now with both engines at their new addresses but "what the Heck?".
-RM
..going to follow this topic. What version DCS are you running?