Two swims this week, one via structured workout - other just normal swim.
Both only recorded the initial set (200m and 400m respectively) and detected no other laps all swim (2000m and 2400m respectively).
Push up and all that is fine as my swim on Monday (3000m structured) worked fine and I have been swimming with Garmin watches across various models since 2018.
Suspecting its a software glitch but cannot be sure.