Sleep accuracy, stress level, BB, watch sensors question... Body Battery and stress level totally wrong..

Hi, 

I tested many Garmin watches over the last months, my overall fave was the Fenix 6s but it was too expensive and too heavy for my needs. Then I tried the very cheap F45s and I was very satisfied but missed the Firstbeat stats. Now I try the F245m and I am quite satisfied. The watch brings many features for a good price, I don't miss most of the advanced features of the Fenix 6s pro. But what I found out was that overall Body Battery, stress level, sleep isn't as accurate as it was when I wore the Fenix 6s. Even the F45s is way more accurate. BB won't charge anymore, after 3h of resting without stress it was loading maybe from 10 to 15. Stress is always high. I feel really well, nothing really has changed in the last month. I know it can mean that I'm getting sick. But to test it I wore the F45s during sleep too and it showed less tress and BB charged around 40 and charges up quite rapidly when resting during the day. During the same sleep my F245m charge only around 10, 30 less. Only charging 10 on BB during a whole sleep with average sleep quality is really a bug. 

Now my thought is, could it be that the more sensors a Garmin watch has the more accurate the overall health tracking features are? Esp during sleep? Maybe movement is shown differently with Gyroskope etc.? But that wouldn't explain why the F45s charges up and the F245m doesn't AT THE SAME TIME! And why the F45s shows less stress than the 245m. 

I did a hardreset an hour ago and will watch it but that isn't a solution in my opinion. 

I don't drink alcohol, eat 3-4h before going to bed, don't do workout 3h before sleep etc. My resting HR during the day is around 48 and hasn't changed, sometimes 46, sometimes 50, but not going up. 

I was a little sick a moth ago wearing my Fenix 6s pro during those days and BB was charging up and stress was way lower than it is now with my F245m, but my Resting HR went up back then because of that illness. That is always the case when I'm feeling sick. And this is also NOT the case with the 245m at the moment. My RHR shows normal numbers. 

Any of you have more watches and a comparison between them or have a problem that BB is rarely charging and stress levels are very high without any reason for it? 

Thank you