File picker in grading an assignment will not load if there is a block_comments.

Replication:

1. Create a course and enrol students
2. Turn edit mode on
3. Add an Assignment activity and set feedback types (tick) feedback files
4. Visit the Assignment activity
5. Click "View all submissions"
6. Click Add block and select Comments
7. Click "Grade" on any of the students record/row

RESULT: The file picker will just show a loading icon and will not load....

Tested as well on https://school.moodledemo.net/