For example creating an external link to a YouTube video may create the error "www.youtube.com refused to connect", and a Kaltura video will produce the error "mediaspace.wisc.edu refused to connect":
This issue notably affects Kaltura and YouTube videos that have been added to Canvas as external URLs. It may also affect other content that has been added via external URL. See "External URL to page that doesn't allow iFraming causes sad face" for more information.
This issue is present as of 8/28/19.
This error can be avoided by making sure you check Load in a new tab when creating an external link:
In general we don't recommend using external links to Kaltura MediaSpace video content. Instead we recommend embedding Kaltura content in a page. Embedding Kaltura media is described in Canvas - How to add or embed a video in your Canvas course using Kaltura Media (UW-Madison) . If you prefer linking to Kaltura content additional information is available in Linking to Kaltura media from a Canvas course.