A new version of the YouTube API v3 Category/Uploader/DLP Filters is available and published in the Online Rule Set Library.
The new rule set blocks further requests created by the browser, to catch video requests, even if the browser is using a cached copy of the video player.

NOTE: Because of how the video is called via JavaScript, calls to the video player no longer receive the video, but receive the block page provided by the SWG.
Currently, the Video Player shows You appear to be offline (or a similar error message), rather than showing the SWG block template.

We understand that this function impacts the user experience. Investigations are ongoing as to whether this behavior can be improved by another change to the rule set.