it tests syllogistic reasoning: Jason's mother was Tyro, whose father was Poesidon, whose father was Kronos. it also tests whether it "eagerly" rather than comprehensively considers something: a maternal great-grandfather could be the father of either one's maternal grandmother or maternal grandfather. so the answer could also be king Aeolus of the Etruscans.

ideally a model would be able to answer this accurately and completely.

LLMs often don't do well on tasks that require composition into smaller subtasks. In this case there is a chain of relations that depend on the previous result.