It's a problem with the camera and phone not agreeing on how to manage the pairing. It appears to only affect phones from Oppo, OnePlus, and any other brand that uses the same oppo/OnePlus version of Android.
My xt-5 was broken by a recent firmware update in exactly the same way.
As far as I'm aware it's a problem with the camera firmware NOT the X-App. It's disappointing (to say the least) that this isn't going to be fixed.
Also the remark that it only works with stock android is nonsense, since there are plenty of people out there with Samsung phones. What they meant was, we can't be bothered to test it on ColourOs.
It would appear that Fuji are, gradually ensuring that ALL their cameras don't work with ColourOs which doesn't seem like the smartest move...