While not at Google for myself a lot of the CI test failures just become knock on effects from complex interdependent CI components delivering the whole experience. Oops Artifactory or GitHub rate limited you. Oops the SAST checker from some new vendor just never finished. Even if your code passes locally the added complexity of CI can often be fraught with flaky and confusing errors that are intermittent or run afoul based on environmental problems that particular moment you tried.