How to stop Surface Interval time after I finish my free dive activity? (the "back" bottom doesn't work)

Is it normal that my Descent G1 solar keep counting Surface Interval time after I finished my free dive?

Up to now, my Surface Interval time is 65hr and 46min. 

I tried to restart the watch but it keep counting. It feels like I didn't totally end the Apnea mode and keep running backstage.

I tried to start another sporty mode but it keep counting. 

Pls let me know how to solve this problem.