Right, I swapped my phone today. This new M8 must have been from a newer batch as all the updates I needed to apply on the 'old' M8 were already on there from stock.
The compass still freezes and the magnetics reading all read zero on X,Y and Z axis.
Sigh...
I'm going to bung some keywords in this post so Googlers will hopefully find this thread.
HTC M8 Compass problem, frozen, stuck, unresponsive, faultly.