(Course creator) The 'File' Content widget doesn't accept files with certain characters in the title
This seems to happen with m dashes (long dashes) as well as parentheses. A problematic aspect of this issue for many users is that the reason for the failure is not explained.
See image for examples. (Note: Underscores are added automatically in place of spaces – ie. these filenames didn't have the underscores initially).
Best case scenario: The widget would upload all files regardless of filename.