Hi there,
Please kindly make sure that you are using the version 6.0.4 of the X and version 3.0.4 of the Cornerstone.
Also, test for possible 3rd party plugin conflict by deactivating all plugins except Cornerstone.
If you still have problems please create a test page containing the Video element and get back to us with the URL/User/Pass of your website using the Secure Note.
We will test the case n your installation and will try to replicate the same case scenario in out local installation. If there is an environmental problem we will give you proper suggestions and if it is related to the core functionality of the element we will create a comprehensive report and will add to our issue tracker for further investigation by our development team.
Thank you,