Click on a thumbnail doesn't change the video.

This issue can be caused by the cache being enabled.

Go to Theme Settings -> Misc, and change the option "Switch Video As" to "Update Player without page reload".

You can also change cache to "conservative" (Global Configuration) is not affiliated with or endorsed by the Joomla! Project or Open Source Matters.
The Joomla! name and logo is used under a limited license granted by Open Source Matters
the trademark holder in the United States and other countries.