Comprehension debt just sounds like there are things you don’t (yet) understand.

Cognition debt means your lack of understanding compounds and the cognition “space” required to clear it increases accordingly.

An increasing comprehension debt that can be paid off one bit at a time within reasonable cognition space takes linear time to clear.

Cognition debt takes exponential time to clear the more of it you have. If it reaches a point where you simply don’t have the space for the cognition overhead required to understand the problem, you probably need to start over from your specifications.