If you get that content blocking purple screen on a Roku do NOT panic and do NOT, at least to begin with, blame the content provider.
A restart of the Roku might cure it without having to bother reseating the HDMI cables.
I got this purple screen for the first time ever, yesterday, when I went to watch the ICC Champions Trophy match #5, viz. Australia v. Bangladesh. I was only getting it on Sling. Amazon was fine. So I assumed Sling had screwed up and all cricket had been banned on Willow due to some licensing transgression.
I was wrong.
Just had to restart the Roku, which only takes a few minutes.
Hope this helps.