Environment: Moodle 4.1.13
Using LTI 1.3, added McGraw-Hill Connect. Professor successfully created an External Tool and deployed an activity (Chapter 1 HW). Then, synched grades from McGraw-Hill system.
Grades successfully deployed. Professor went into Gradebook, edited grade item for one student, added a comment to "Feedback". In User View, the assignment grade is now not visible - the whole row for that assignment is not visible - but the category grade accurately reflects the student's grade.
Hiding the grade item, then making it visible did not change this behavior. Deleting the feedback comment (including all the hidden HTML) did not change this behavior. Multiple attempts to make the grade item visible in the User Report failed. Ultimately, the professor deleted the activity and recreated it.