Using the thumbtime parameter for creating a time based thumbnail is not working correctly. The resulting thumbnail always shows the frame from the middle of the video. Also template:Motd/ thumbtime is affected (see https://commons.wikimedia.org/wiki/Template:Motd/2017-07-03_thumbtime).
Revisions and Commits
As far as I can tell, it has to do with Varnish or Swift URL-encoding the request, where thumbor expects "seek=4" and gets "seek%3D4". All the existing integration tests are Thumbor only, without Swift or Varnish in front of it.
Files with thumbtime thumbnails "stuck" to the wrong time should be fixed by being purged. Make sure that you clear your browser cache as well (shift-click on a page where the offending appears) to see the change after purge. I've just purged the video from the task description and it worked fine.