Why does my ultra endurance ride not contribute to training load or training readiness.

Have you checked your Max HR and LTHR? I've not yet done the maths but my reported LTHR erroneously increased to 188 (from 166) a couple of weeks ago and seems to have thrown out all of my Training Load calculations.

so... I should just stick to Strava to monitor my training load?

As I mentioned in the original post, the activity was recorded on my Edge 850. My X1 watch provided HR and Sram Power meter.   This was a continuous activity.  We paused for 3 meals and a few nature breaks.  We rode through the night without sleep.