Apple Watch 10 swim not recording accurately

I have a new Apple Watch 10 and it is not recording laps accurately. I had an Apple Watch 3 which did record swim laps so the setting in the 10 are all downloaded from that watch. The pattern of error is odd. First, I swim a kick lap, and the sets of 300 or 600 alternating with a kick lap. The watch gets the first couple or set correctly and then it goes wildly over. For example, today I swam 2000 yards and it recorded 2400. Help!