I am experiencing the same issues. All my problems started with update 2.39.20. I bought the device in June, and everything was perfect until the update. The issues began with the heart rate monitor not working (it usually stops during the night). Now, I have additional problems with sleep tracking. I slept really well for 7 hours, but on the watch, it was marked as a 2-hour nap and 3 hours of sleep.
I’m sending logs to suunto, hope this will help.