Danny,
I don't want to sound condescending, but I imagine everyone posting in this thread has already seen your recommendation provided by the support page back in June of last year and tried it IT DOES NOT WORK long term. It will fix the issue once, and then when you turn the TV off and back on or change sources and go back to the HDMI input the Roku is on, it does NOT reestablish/reauthenticate the HDCP connection.
When does the ROKU authenticate HDCP? Is it when the Roku is powered on? Is there ANY OTHER TIME when the Roku re-establishes HDCP?
Here's the summary:
TV set to Roku input. Roku restarted. HDCP works.
Change TV input to antenna or other HDMI. Roku still on as soundbar so RECEIVING AUDIO OVER HDMI from other source (antenna or DVD or whatever). Go back to Roku HDMI as input. HDCP does not work. Restart Roku via menu on Roku, HDCP works. (hence cable and connection is NOT the issue nor is TV) Roku is the device delivering the protected content, it is the issue.
TV set to Roku input. Roku on. HDCP works. TV turned off while still set to Roku input. Roku goes to idle or whatever happens after no input or use for a while. TV turned back ON. HDCP does not work.
The issue is whenever going BACK to the Roku video stream as an input, the HDCP authentication DOES NOT get re-established after at some point the authentication was done and worked (the authentication probably drops out when TV is turned off or source is changed at TV to other HDMI and now the TV is using the ARC functionality to send audio back to the Roku soundbar).