The problem (HDCP Error Detected ...Error 020) occurs when using "Roku Media Player Version 5.5 Build 9" to play a UHD 2160p source material from my new Roku Express 4K+ to a 1080p TV. I get the same result on a 1080p TCL and a 1080p Sony TV. This same Express 4k+ and SAME CABLE plays same content OK to a 4k UHD LG TV.
This arrangement successfully plays lower-res 720p content fine to all TVs.
My Roku Ultra, using "Roku Media Player Version 5.5 Build 9" plays the content successfully to these 1080p TVs. My defunct Roku 3 successfully played this content to the 1080p TVs.
The Express 4K+ seems unable to use Roku Media Player to drive a 1080p TV from UHD source material.