I have the 235 with the latest firmware 126.96.36.199. During an outdoor run on the 23 February I noticed an issue with the heart rate monitor freezing during activity, I had not experienced this two days earlier during a 5x5 min exercise. It got stuck at a heart rate of 186, which is around 10 bpms away from my max for almost one hour. Today the same thing happened, it got stuck at 159 for around one hour during a 5x5 on a threadmilll, in reality I was probably moving bewteen the 160s and 180s. I tried to both tighten and loosen the strap to no effect.
So, does anyone know what's going on? I did try a restart after the first time, no result. Do I have to do a factory reset? Or is has the whole thing gone bad and needs to be replaced? I've had the watch for just 9 months.