throw the switches inside the engine to make sure they're not stuck halfway. ( make sure it's set to DCS and 3 rail)
Try adding the engine on a short piece of track as the only engine powered up. Sometimes the remote sees another engine and gets confused.
Make sure it plays shutdown sounds for a few seconds when you cut the power. If it doesn't, I believe the remote can't add it properly.
I would still tether the remote incase something happened recently.