Rest timer skipping random seconds

My Swim 2 is 3 months old. I have noticed that in the last couple of weeks that the automatic rest counter for pool swimming is not counting correctly. It starts off fine, but then jumps random numbers, and at random times. So, it counts 1, 2, 3, 4, 8, 9, 11, 15, 16 , 17, 22,...
It is also no longer accurately detecting my stroke type. I looked back on my earlier workouts using the watch and the detection was correct.
I have done a factory reset on the watch and the problem persists.
Is this watch faulty and should I send it back, or is there a setting that I need to adjust?