Hi @111664890950382,
Thank you for the video of this.
Do you follow steps that someone else took (CelestialDawnA, I have intentionally not "tagged" them because I do not want to notify them but their profile is located at https://community.canvaslms.com/t5/user/viewprofilepage/user-id/2948676) in the comments of the question at https://community.canvaslms.com/t5/Archived-Questions/ARCHIVED-There-was-a-problem-updating-the-subm...
They left a long comment with a "TL;DR" ("To Long, Don't Read") section that says:
TL;DR: Change the "Assign To" settings to list one particular student, save the change, then go back and edit the "Assign To" to be set to "Everyone" again. Saving that should reset the issue and bring back the ability to modify their scores.
If that does not work, you will need to report this directly to Canvas Support instead of as a question in the Community.
-Doug