Electrical issue-makes no sense

[RobertInOntario]

Two questions:

Are your rail joints soldered?
Do you have feeder wires to each section of track?

If not, perhaps glue got into some of your rail joints - insulating them.

The same thing happened to me with my larger layout, and it really baffled me at first too! AFAIK, the best way to resolve this is to solder the rail joints in the sections where the locos stall. The glue / water mix almost certainly got into the rail joiners.

Rob