seems very likely to me that the chromecast is blocking some websites from being able to stream. (mostly ones on the other side of the law)
form chrome on several different devices, i can cast youtube and netflix no issues and I can mirror my tab (although laggy) with no issues but trying to cast from the website itself will appear to connect, load for 2-3 seconds then disconnect the cast. I am almost positive this is an intentional block by Google as its happening to 20 or so websites I have tested.
Has anyone else experienced this? and blocking google dns makes no difference either.