During the pool swimming activity the Epix watch detects the Backstroke as Breaststroke almost all the times. I have confirmed this flaw with other swimmers that use various Garmin watches. I have got the same wrong results with my old vivoactive 3 watch.
I would suggest Garmin adding an option to manually select the correct stroke type in pool swimming activities. Otherwise Garmin should improve the algorithm that detects the stroke type.