BeatsX problem switching between apps

IPhone 8, iOS 11.1.1

Beats X connects fine with my iPhone but when switching between apps - especially FaceTime and others, it’s unpredictable to use the BeatsX. This is very inconsistent and troubling. I have reset network settings, turned off Bluetooth on and off but frequently I just can’t hear anything and the microphone also does not work through the BeatsX even though it’s selected everywhere. Any ideas ?