Politzer makes minor misunderstandings of internal contradictions. This is rectified in my list by adding On Contradiction right after, but taken as a single source of dialectical materialism, it can lead to errors in how we view contradiction itself, resulting in vulgar dialectics. An example is when Politzer characterizes the crushing of a flea as not an example of autodynamism, instead characterizing it as external and mechanical, while Mao more accurately shows that the winner and loser of a battle is determined by their internal characteristics.

This is a decent thread going over it, along with debate around Politzer's understanding and dialectics in general. It's actually what's prompting me to take a detour from Capital Volume 3 and revisit dialectical materialism to patch up holes I may have.