Not sure if anyone else is still seeing the same HR issue on the most recent software update?
I was seeing improvements on 18.20 and 18.21 with shorter runs of 5k, however have just finished a 10mile (16k) and noticed the heart rate jump occurred again at kilometre 7 - a clear jump from 150ish bpm to 188/190 and then remained there for the remaining 9km left to run!
Starting to get more than a little frustrating now!!!