mod_assign: Unable to scroll grading page on mobile

When I open a mobile site and I want to grade assignment, I cannot scroll up/down on mobile phone.

However, when I start dragging the contents early enough before page finishes loading, I can do that! But after page loads and I release the finger, I cannot scroll anymore. I suspect that some JavaScript blocks scrolling after page loads.

Luckily this can be replicated on Google Chrome in Windows.

1. Login to Orange School demo: https://school.demo.moodle.net
2. Navigate to: https://school.demo.moodle.net/mod/assign/view.php?id=661
3. While using Google Chrome right-click on the page and select "Inspect" from context menu (Ctrl+Shift+I)
4. In "DevTools" window enable device toolbar to emulate mobile phone (Ctrl+Shift+M).
5. Select "Responsive" or "iPhone 6/7/8".
6. Confirm that scrolling works, by clicking on the page and using dragging gesture.
7. Click on blue "Grade" button, or navigate to:
   https://school.demo.moodle.net/mod/assign/view.php?id=661&action=grader
8. Try clicking on the page and dragging the contents - it will not work
9. Refresh the page using F5 and immediately click and hold mouse button (don't release it yet!)
10. Wait until page loads and then use dragging - it should work !
11. Release the button and repeat 8. - it will stop working.