Sleep and HRV not tracking

I have a pretty new Forerunner 265S and it's been working fine until 4 days ago when the sleep tracker and HRV tracker stopped working/only working partially.

- HRV is not being measured in the night or partially, resulting in incorrect results for my training readiness

- Sleept tacking is not being measured or starts way too late, resulting in incorrect results for my training readiness and sleep score

I saw this was a previous issue and wondered whether anyone had any solutions. I've tried all the obvious ones ie. switching on and off, checking the strap is on properly (nil changes), plugged it into my laptop etc. 

It's really bugging me because it's offsetting other scores and then getting mad at me whenever I do a workout Joy

Thanks in advance for any help!