Fenix 6 Pro - Battery Dead during sleep

Hello guys,

I am having Garmin Fenix 6 Pro over the last 3 months and suddnely over the last 2 consecutive days, when I go to sleep at night (with the watch charged aroung 30% - 40%), the next morning I wake up the watch is powered off due to full battery drain.

Any ideas why could this happen? 

THank you in advance

p.s. I have been wearing the watch over sleep during every day the last months without any problems like the one above