I have this issue as well. Last night I tried to reboot the watch as the battery seemed to be abnormally draining. I have to do this once a week or so. Once the watch shut off. I could not get it to restart. I tried the normal power button. No luck. Both buttons.. nothing. However if I toss it on a charger it seems fine. I'm going to let it drain out. i tried this once before a few years back when it did the same thing.. hopefully that works. but is there any ideas of a fix? Thanks.
I have good news. First of all im in Australia but im guessing this issue is workd wide.
I came to this forum because i was having the issue with my back/power button nor working.
Having to shut watch by pressing both buttons at the same time and turning it on the same way.
I reached out to Samsung Australia. My watched was bought in jan 2018. The operator was very friendly and told her my issue. She raised a work request for the watch. I send it to repair on Thursday 23rd of July. Got it back today Wednesday 29th July. I sent it by post service.
Watched came back with the button now working.
Repair Discription is, REPLACED PBA, Battery tested OK.
It was repaired under full warranty.
So I guess my advise is reach out to support and explain your issue. do all the trouble shooting before hand. Not much can be done but at least upgrade software if you havent, and also factory reset the watch.
Good luck to all