Looking at the picture, I would think that you would feel it happening if it is a burn of that intensity.
I would expect that you find out it is an allergic reaction instead.
I have same problem since update. Replied to another message to a Samsung person with a photo. No response. Just did a chat with support. They said to not use the watch anymore until someone from their team can contacts me. They say it's due to safety issues. That is concerning!