Showing Dexcom reading on Garmin watch - intermittent data problem

I have a Garmin Fenix 6 Pro watch and I am trying to get the Dexcom widget up and running to display glucose levels on my watch. I think I have done everything right in terms of setup, however the watch only displays data intermittently.

See the photos - it's strange as sometimes it will display the glucose level and arrow fine, but then other times it simply says "No Data". I am using a Dexcom One sensor.

I am hoping that someone on here using a Dexcom / Garmin watch combination will be able to help me out.

Many thanks

Dave