Trying to unpair controllable trainer results in crash to desktop with no error msg

I am using an Elite Directo trainer. This trainer appears as two different trainers to zwift, an FE-C trainer and another one, only the FE-C option works properly, with the other trainer selected as controllable trainer I get no resistance change when going up/down hills. Trainer used to work fine and only had these issues for last few weeks. When I try and unpair the incorrect trainer which seems to pair by default, Zwift crashes to the desktop with no error message or anything. The only way I can get the correct trainer paired is to power off the trainer and then start zwift, once at pairing screen I can then power on the trainer and quickly pair it correctly. However when next starting Zwift, it defaults to the wrong trainer and I have to do the whole mucking about again.
Thanks, lee.