MTH Steam Engine Stalls at AtlasO Switch

voltmeter reads correct voltage on the switches where it stalls (about 16-17 volts), consistent with Z4000 display.

I have had a similar issue in the past, but the problem was the common, not the center rail. Basically an interaction between insulated rails and rubber tires. Recommend you split the dictionary - with the engine in the stalled position, use a test lead and connect one end to a known good common and the other end to the wheels. Another option would be to remove the shell and touch the end of the lead to the black power lead in the truck. You can also do the same test but connect one end of the test lead to a known hot center rail and carefully touch the other end to the red wire attached to the center roller in the truck.

Thanks.  The same engine runs fine going the other way.

I will try your suggestions.

If it's the center rail, you can add a roller to the tender. MTH Switcher Reliability Upgrade

Many times it's even simpler than this mod.  If the tender trucks are pre-drilled for pickups, adding one is trivial.  If it's the outside rail, you can also add axle wipers to the tender and enhance the grounding.  I've done both of these modes to various locomotives.