How can I fix erratic heart rate readings on Apple Watch?

My Apple Watch has started producing very erratic high heart rates while on a walk/ run. Especially but not only happens at start. Of run- zooming up to heart roof c160 but when I take it myself it records eg normal level of c 1-5. Happens at intervals when using Runkeeper . happens more frequently. Is this a software bug?

I’ve done all the recommended steps re strap, fit etc.

a lot of people have reported similar problems but I can’t find any actual resolution.

Any advice please- apart from binning the watch and returning to my trusty old Fitbit!

[Re-Titled by Moderator]

Original Title: Erratic high heart rate readings