Solutions to Not Saving Changes in SharePoint List or Library

1. Check if you have proper permissions for the list/library
2. Verify that you have adequate right item level permission for the item you are trying to update
3. Check if the required fields in the list/library are properly filled.
4. Verify that the list does not have unique or partial validity constraints i.e., user is not trying to enter a value that already exists in the list
5. Finally, verify that you are trying to update the correct list/library.