Ant+ on iOS issue

I’m attempting to use the wahoo ant+ fitness key & Lightning 30-pin adaptor for iOS version 11.0.3 (iPad Pro) and transmitting heart rate via my garmin forerunner watch. It works for about 1 minute before freezing the heart rate number in Zwift - is anyone else seeing this behaviour?
I’m forced to then quit Zwift and swipe to restart but after getting a new ant+ signal it freezes again shortly into a ride.

This setup works ok testing on the wahoo fitness app so assume a Zwift issue?