Why "had broke" breaks grammar rules

What kind of error is it?

It's a grammatical error related to the misuse of verb tense.

Why do people make this mistake?

People often confuse past tense forms with past participle forms, especially with irregular verbs, which can lead to incorrect combinations such as "had broke" instead of "had broken."

What is correct?

The correct form is to use the past perfect tense by pairing "had" with the past participle of the verb, which for "break" is "broken."