"Will samsung replace my watch as its under guarantee?"
Yes, they will replace it with another watch with the same *hardware* issue.
Stop wasting your time and get a product that works. I have: my Fitbit Versa works as advertised, especially HR monitoring. It doesn't *miss a beat!*.
Get a refund and don't look back. I haven't.
It seems I may have fixed my Gear S3 flatlines by removing the Samsung health widget with hr reading, burnt calories, steps and floors. (It has recorded last 2 walks correctly) I suspected they messed up something with widgets as the weather widget was blocking other apps from acquiring location. Tomorrow will probably verify if my issue is really fixed cuz I havent got a full reading from cycling to work before, always flat lines.
I got hr graph in negative after running and sync like this but while running can show hr rate on watch. what should I do
ps. gear sport and S health on iPhoneX ios 12.1.4