I had exactly the same problem, it didn't display heart rate while pretty much doing anything but sitting. After the update I got today, it is fixed, heart rate was working during my run without problems.
Well, I spoke too soon. While yesterday I was able to do short run and some hiking and saw somewhat accurate heart rate, today in the gym it was almost as before. At first I didn't start workout on my watch, during warmup it was showing 185, probably 2x actual heart rate. Later I started circuit workout in the watch and during heavy deadlifts it was showing 60 and then stopped altogether. I tried to restart workout multiple times, so I noticed, that heart rate app shows at least inaccurate heart rate if it cannot measure it at the time, while workout app shows - -. In short it sucks maybe a bit less than before, at least you can go for a walk and log your heart rate somewhat accurately, but during workouts it's totally useless.
I have the same issue. Whenever I work out or do anything 'active' my watch will say my HR is 220. Holy *****! Scared the heck out of me, thought I was having a heart attack! Glad to learn this has happened to others and I'm (hopefully) not dying.
Still very weird that this watch frustrates the hell out of me, they apparently from all reports have an update but I can't get in in NZ! Why not? Samsung have done incredible damage to their reputation over this matter but why?
I bought the Galaxy Watch 46mm and the same strange things happened all the time. When you stay still it measures the pulse fine when you move stops immediately. I even shave my arm, tighten the strap, little improvement, but still when you move stops to measure the pulse or get incorrect values like 216 bpm or as low as 29 bpm.
I came from Fitbit Charge 2 and there are none of these issues.
Tizen Version 22.214.171.124
Software Version R800XXU1BRK3
When you go for a walk...