I was writing some more than we had a power cut.

There is a viewable parameter called 'H' which shows the absolute position of the shaft. This isnt reading what I would expect. It flickers between, 1, 3, then 4096 then back. It's like it is on the index but ultimately then it doesnt seem to move when the shaft rotates.

I'm not sure if any of this could be due to the way that I am powering this (via a VFD via a choke) however when it stops running (after the stop signal) its ultra smooth.

Will keep looking.