Apparently once you add a "Grading criteria" text, the model collapses into a "compressed toward the center of the scale" hallucination (or training set overfitting).
Someone on X asked me to try to reproduce it, and I actually got it on the first try on their Gemini Chat:
https://x.com/XCSme/status/2057613611959279988
I am not sure what to make of this (or most SOTA) models. They got a lot smarter with coding and tool usage, but a lot dumber in other ways...