I also had the stock cam app locked on the front cam since weeks on my XA2 single 4.5.0.19 with the difference that the switch button was visible.
It was working perfectly in adva’ced camera.
Many thanks @attah for the hint. That solved it instantly. Sorry that it doesn’t help the OP.
About the OT, can a camera be unplugged, inside? (as the phone doesn’t seem to even see it)