OK, are you running DCC? Try running affected locos on DC only, turn the other controller off (cut the power off). I’d suspect a problem in the locos, but try to rule out any electronics issue first. That seems strange, 2 engines crapping out at the same time. If they still act up with only the MRC 1300 turned on, then time to start troubleshooting the engines. If they run fine, then we’ll need to do a bit more testing to see what’s up.
Brad