Rest

Still got cold!
I did get seen by Ben Hallum today (bespoke cycles) - he made up my cycling insoles about 6months ago. An expert in bike biomechanics he watched my cycling and we tried to get to the bottom of my feeling wonky when fatigued. At last I have something to work on;
I do indeed have a tendency to rotate to the right.
This is due to a tight piriformis on the left
To compensate my short right adductor and right TFL have to internally rotate my right leg at the top of the stroke to bring the right leg into the midline.
This also makes me sit towards the left side of the saddle.

Solution
1. stretch the left priformis
2. stretch right short adductor and TFL (IT band)

When cycling shift to the right to stay in midline.

The expensive bike fitters would shim the left cleat, and wedge the right but this doesn't really fix the problem.

As always a lot of this should start with "probably" as I now know different "experts" have different opinions - at least I have something to work with now though.