apple watch recording activity and stand hours in the fure

for the past 3 or 4 weeks, my apple watch 3, latest OS, has been recording exercise minutes and stand hours overnight for the future - for example, when I wake up in the morning I see 50 exercise minutes and 2 stand hours recorded at around 5pm . I wear the watch at night.

during the day it seems to work ok, only recording activity and stand hours when I'm actually doing something - see screenshot, - it's only 12 pm, but there is activity around 6pm