I'm hoping someone here can re-write this for helping others if you agree with it.
I've had more than one engine now and even an upgrade, if I remember correctly?, that has needed a conventional reset to run correctly. The most recent one, actually shocked me. It was right after upgrading my TIU and trying to run an already built consist, where the lead engine got locked in reverse. I've had another that right out of the box needed a reset. Finally, I'm thinking that an upgrade I did myself, needed a reset after installing a soundset where it just didn't take fully. The reset got it straightened out and running correctly.
So I'm thinking that this should be a go to idea for engines that appear to be locked up when testing in conventional mode. Maybe an engine that won't add to a remote for example, should be tested in conventional mode to see if it exhibits this behavior.