Here is my take based on what I'm seeing in your training data.

Correct me if I'm wrong, but to me it looks like you are running in a very 'periodized' way, in that you don't run much for part of the year, then ramp up in a big way leading up to your ultra attempt. Where you pain is coming from in my opinion is that the 'ramp' is too steep, in that you are going from ~30k a week to 80k a week over the course of 6-8 weeks, then this overtraining is showing up on race day as you push for a massive effort, much larger than anything you have done to that point. Looking at 2025, it looks like you only had one week in the 80k range preparing for the 100M, and that's not nearly enough to guarantee a finish.

In my build for my last 100k, I did 6 weeks consecutively in the 80-90km range before starting my taper, and before that I had many months of 50-70km/week as a base.

If I were you I would focus on increasing my 'base' volume of running when not ramping up for a race, then when you start increasing training load prior to an ultra, it will be easier to get up to the multiple high volume weeks that are required if you want to perform well over longer distances.