iOS 13.4 Bluetooth Connection Problem

So, brand new Fenix 6X Pro. It simply won't connect to my iPhone X Max running iOS 13.4 beta. Tried all the usual stuff, turning bluetooth off and on. Turn the phone off and on. Turn the watch off and on. etc, etc.

Decided to try on my wife's phone. She is on the previous iOS version. Using her Garmin account on her phone, my watch connected straight away. 

Went back to my phone and again the watch won't connect. 

Anyone got any ideas? I think it might be that my phone is on different iOS firmware.