Vivoactive 4 adding mystery laps while pool swimming

Last week I purchased a Vivoactive 4 after my Apple Watch finally gave up.

The Apple Watch was always accurate recoding my pool swims over a 3 year period.

in the space of 6 swims 3 times the Vivoactive has added mystery laps to my swims.   I’m a very slow swimmer - approx. 3 mins / 100m.   When I look at the resulting graph afterwards it’s showing occasionally I’m doing 100m in 50 seconds which is just ridiculous!!!

Is anyone else experiencing a frequent inaccuracy in their Vivoactive 4?

its very disappointing after 3 years of no issues with my old Apple Watch. 

Michael