Erratic hearth readings and high stress levels

The problem started like 10 days ago when the heart reading went somehow erratic and the stress level over the clouds with 50+ all day long, even while sleeping.
After resetting the watch 3 days ago everything came back to normal with a normal heart reading and stress level under 30 as usual (at least for me).
The thing is today I woke up to find out once again erratic readings during the night. While sleeping PPM jumped from 40 to 70, 50, 40 and 70 under segments of 20-30' and stress levels over 50.
This is a known issue?
Ver software 21.00 (411945a)