Hmmm, ok,
This is happening to all your locomotives right? What brands and type of locomotives?
Do the locomotives loose radio contact if you don't try to move them with the throttle? ie selected with the HC but just sit there, don't try to move them forwards or backwards.
You mentioned 8 pin plug so I'm wondering if there could be something about the board the LM's are plugged into. While it isn't impossible you could have a flaky HC I wouldn't think that'd be the case.
- Tim