Apple Watch Series 5 locking it self on wrist

Hello, I recently bought Apple Watch Series 5, updated to the last iOS and found my watch keeps locking despite on wrist. I tried reset it, setup as a new watch but nothing helps. I have had apple watch 3 before on previous watch os, and it’s never happened. It happens when I unlocking my watch on wrist, put my hand down and raise up, then after second watch locking it self. I have installed public beta 7 after all, thought it will fix the problem, but it’s the same behavior.