The watch lost 9% body battery during a 2min health-snapshot, just after I woke-up!

Frankly, your stress is quite high (during sleep too) and there is a gap in stress readings between the health snapshot and the last known stress reading. The last known stress reading is a high stress period and there is a chance that the watch could have just extrapolated the stress levels from that time to the time you took the health snapshot and reduced the body battery accordingly.

I was a little sick... yeah I know that :) - regarding BB% , woke-up, went to bathroom, did a snapshot... I never seen something like this before on any GARMIN watch I've owned... The -9% bb drop was actually shown in the health snapshot, only on the watch... anyway... These seem just bugs, as I used 3+ years other watches, never filled a ticked or needed to post on forums... they just worked... These new garmins/software are just bonkers, it's hard not to be irritated, doesn't make sense... too many errors... :/

I just experienced the same, made a snapshot before going to bed and lost 9 BB, my Stress level was at 15 before and after. Looks like a bug to me.