Fitness app no longer syncing with Garmin Connect

I have been using the Fitness app (not the + version) on my iPhone mainly for a bit of fun. It was syncing with my Garmin connect app to log cycling etc but for some reason it has stopped doing this. I didn't change any settings and cycling remains selected in the health app.

It's a bit ridiculous really (but proves how effective the psychology of it is) but it means that on days when I cycle a lot and walk less, my move ring isn't closed. And it's annoying me!

Does anyone know how to get it syncing again? Even better, how to get it to do so retrospectively and close all those move rings?

I don't have an Apple Watch, but it DID sync up previously so I know it's possible!

Thanks in advance

Dominic