Does Bill Clinton provide your definition of 'primary'? Because it was problem with the Max which appeared early.
From May, 2017: "Boeing grounds 737 MAX planes over quality issue with engine"
https://www.seattletimes.com/business/boeing-aerospace/boeing-grounds-737-max-test-planes-over-quality-issue-with-engine/
The apparent cause of the two recent crashes; apologies for not making that clear as I thought most would pick up what I was referring to the last several months.
Engine failure would involve CFM International who built those, not Boeing directly.