Fenix 6 Pro + Wahoo Tickr Not showing live heart rate during activity

Using my Garmin Fenix 6 Pro on my road bike (mounted to handlebars) with Wahoo Tickr chest HRM. Has always worked fine and last use was only three days ago with no issues

This morning I started the watch & HRM as normal and took off. I soon realised while cycling my heart rate was just showing whatever it was when I started cycling, it was essentially frozen. I stopped to look into the issue and all of a sudden my watch started showing the real heart rate - jumping from 90bpm to 120bpm instantly. As soon as I started cycling, the heart rate data essentially 'froze'. After 3-4 road side stops to try to troubleshoot the issue, including removing HRM, disconnecting and reconnecting HRM to the watch, and starting a new cycling activity on the watch, I gave up.

I've had my Fenix 6 Pro since December 2020, it's up to date and everything else works as you would expect.

Any suggestions would be much appreciated as this essentially renders my HRM & training to heart rates useless.

Thanks!