If you're not seeing the student grades for the pre-test in the gradebook, that's perfectly normal. Stop pulling your hair out. You're not going crazy. Any pre-test that a student completes is auto-graded by the system, but the pre-test is not factored in to the student’s overall grade. So when you go into the gradebook it by default only shows you things that count toward the overall grade average.
But wait! There is a check box at the top of the student or content page in the gradebook that says, "Show Only Graded Assessments" which you can uncheck to reveal all course content. It’s a weird phrasing, I know, because technically the pre-tests are graded by the system, it’s just not including the score in the overall grade. It’s being treated like a reading or video page that is also not graded. Does that help solve the mystery of the invisible pre-test grade?