Major Issues

[andy.chandler71@gmail.com]

Can you swap out the decoder in those locomotives with a known good one?

If I have a decoder that will fit. I have to check my supply. I do not have any sound decoders.

Is it always the same place(s) or similar places? Drop a marker where the problem is, and see if you accumulate a lot together.

Sounds like a good idea.

Try factory reset of decoders first.  CV 8 I think