OWS - terrible GPS

I’ve just had a chance to start open water activity on my new Descent G1 Solar. I really hoped it would behave different that Instinct Solar 2 Surf which I also owned and unfortunately had to return for same reason. I always start activity after GPS is locked and only then enter the water. Usually around 1 minute after entering the water GPS lose the location and my watch records only the other parameters like strokes, HR, time and temperature. So instead of I.e. 300m I end up with 7 meters swim. Same happened on GI2 Surf. I swim only crawl and prior to having those watches I had Fenix 6x and Instinct 1 - there were no problems with recording my swim length (same condition, same swimming style, same settings). 
Does anyone have ideas as to what can be the reason for this? I really don’t want to send this watch back. Please find below my activities: 1st one is from Descent, the other two are from Instinct - all of them should have the distance of at least 250m. 

https://connect.garmin.com/modern/activity/8646916541

https://connect.garmin.com/modern/activity/8392224781

https://connect.garmin.com/modern/activity/8380420148