Hi all,
After a year of 5+ ownership, I was recently plagued by the button issues that others here have frequently complained about. The start/stop button had become stiff and it felt as if there were a double clicking action, followed by the button seemingly become jammed down when depressed.
The theory was that some dirt, oil, or a mixture of the two may have worked its way into the button mechanism and was jamming it up, so I've soaked the watch in a bowl of warm soapy water for 30 minutes, pulled it out and clicked the button multiple times then repeated the soaking processing over the next couple of days. True enough, whatever was in there broke down and the buttons were freed and feeling like they did when the watch was brand new.
I'd advise trying this if you experience something similar.