Hello,
I don't know if it's a coincidence but after the windows 10 update 2004 the preview in the "cut section" no longer works.
I can only see only the wording "Video Preview" and the keys to move forward and backward have no effect on the cursor.
Try to update to new version 3.0.22. That should fix the issue.
If not, disable "Use fast sample grabbing" under Settings/Preferences/Preview.