The issue is evident now. It wasn't before because the original mp4 in VP preview and the export looked the same.
The problem isn't with the overlay. There's something about the mp4 encoding that causes loss of contrast, and this is seen in several editing programs.
For the fix, that file was captured, then overlaid with a sync-corrected and cropped insert.
See your Personal Message for the downloadable result and project zip file. Click the envelope at the top-right of this forum.