@temafey There a number of things to remember if you want to have better swimming track results:
Water doesn’t transmit GPS signal so you can get track only if you’re swimming freestyle (crawl), not breaststroke or anything when your hands underwater for long periods
Enable workout mode at least a couple of minutes before actual start so watch acquires best signal
Do not make pauses in water during exercise. If you pause while you’re in water and your hands under water during pause - watch is losing signal. After you continue your swim it takes time before watch gets GPS fix again.
Experiment with different GNSS combinations. While for running almost any GNSS is okay nowadays, it may have an effect for OWS.
Try putting watch on different hand
The only way to get perfect track/distance in open water swimming - is to use Swim Buoy and put watch in it.
These are mine recommendations, based on my experience. Suunto also has some on this page https://www.suunto.com/Support/faq-articles/lifecycle/how-to-get-more-accurate-open-water-swim-tracking/