For those with problems with the right button. The same thing happened to me a few days after getting the watch, and I can confirm that it's a hardware issue.
I opened the device and found that the switch had two of its four pins not soldered. I've been able to fix it with the right soldering tool, but the watch not easy to open. I'm a STM engineer, IMO when that soldering defect happens, it can affect large batches of a production.