Even this hasn't never been perfect and missed/added lap or two during my 60 laps sessions, I could live with it. But recently it counts like every 4th lap or so. Last time it counted 15 laps in my 66 laps session. There was neither firmware change/update nor my swimming style (maybe I'm doing the turns more precise and smooth but it's not very significant change either).
However I use also Amazfit Stratos and they count it almost perfectly (even they miss the turn from time to time, they can manage to recalculate it from time and strokes ratio) so I'm thinking if it couldn't be hardware fault in TomTom case.
Does anyone have similar experience?