I have had this exact thing happen to 2 MTG's (both were the original 4G MTG). In both cases swapped them out with a new MTG. I have swapped ethernet cables, tried different antennas, swapped displays, factory reset display, inplugged power to MTG, in the end replaced MTG, then things started working. In both cases, the problem happened after an update (the first when updating to 24-2, the second when updating to 25-1). I think it is software related and there has to be a way to recover them, but with the promotions for MTG's they were running, it was cheaper to replace then troubleshoot.

If anyone figures out how to fix the MTG, let me know, I would like to get these two MTG's working properly again.