Atlas Trainman RS-3 latest run

Look for a broken wire.

I agree on the possibility of a broken wire at the pickup roller.  Sometimes a weak solder job is revealed after the trucks turn on a few curves and the wire breaks loose.  Follow the wire to the break.  BigRail.

You can check for a broken pickup wire without opening up the engine.  The rollers are connected to the same location inside the engine.  Normally, there should be a direct connection between the rollers and would show up as a "short" on an ohm meter.  If the connection is broken or "open" you'll get an infinite resistance.

Jan