If you're not seeing the student grades for the pre-test in the gradebook, 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 have your gradebook filtered to only show "Items That Count Toward Grade" the pre-test and similar content items that don't count toward the student's grade are NOT displayed.
Look to the top left of the gradebook page for the Filter icon next to the word Chapter. Click that and uncheck the option for "Items That Count Toward Grade."
It’s a weird phrasing, I know, because technically the items that count toward the grade are always displayed, but checking the box hides items that are not included in the overall grade.
Does that help solve the mystery of the invisible pre-test grade?