I have the Roku 4k+ stick. I was and am still getting HDCP error code. After doing my own testing I figured out the following.
There is a power setting where you can enable it to turn off Roku after 20 minutes of inactivity. What I have found, is if you enable this setting, Roku shuts down. But when you go to watch anything(Netflix, Hulu, etc.), you will get the HDCP error code. You then have to restart Roku device and if fixes the problem.
However, if you do not enable the 20 minute power setting, you will not get the HDCP error code but since the Roku stays on, it drains the remote battery causing the problem of why users are having to change batteries so often.
I tried to report this to Roku support in chat but they just decided to send me a new remote but it won't fix the problem. I hope who ever reads this will test to see if the same thing is happening to you.
I believe it is a software/engineering issue with the power setting.
I go to Settings-System-Power-Auto power Savings. Can enable "After 20 minutes of no interaction." If I enable this, when I turn my tv off at night Roku will shut down and in the morning I will get the HDCP error code when I go to watch lets say HULU. I then have to restart Roku and it fixes it.
If I don't enable this, in the morning when I turn on my tv, there is a screen saver and I can go into any app and start streaming. However it will drain your remote battery. I tested it for two days and confirmed my suspicions.