Galaxy watch 7 sleep stages stopped working properly

[Yiftach]

I use my galaxy watch 7 for about a month now. in the first 3 weeks the sleep tracking seemed to work great (see snapshot for example ).
But In the past few days it seems that something went wrong. The sleep stages no longer make sense. Too many flat areas, and sometimes the sleep time is split into 2 periods with no apparent reason (This was only shown on the watch), and only one sleeping cycle.
See here for example:

I set the sleeping mode on and off manually when I go to sleep and when I wake up.
I also set the watch on flight mode when I sleep, but that was all along, when it worked fine as well, so I don't think it is related.

Anyone knows what could be the problem?
Thanks

[JordanS · Accepted solution]

For accurate sleep tracking, make sure the watch has a snug fit overnight, and you have your Heart Rate tracking set to continuous under Samsung Health > Settings > Heart Rate. It's worth giving the sensors a good wipe down and if you haven't restarted your watch in a while, give a restart.