Just thought I would share this advice with others, incase anyone has experienced similar issues. In my case I never realised this fix until I did it coincidentally!

My previous setup was a Samsung tv, Samsung soundbar (connected to tv via Bluetooth) and Apple TV.

I was constantly getting HDCP errors when using certain apps on Apple TV, with the only way to resolve it resetting/rebooting the TV or switching it off at the mains. I tried various settings and HDMI cables and nothing helped at all.

Recently I switched to the HomePod minis in replace of my soundbar and to my surprise, the issue has completely gone away since this.

My conclusion being that having my soundbar connected via Bluetooth to the TV must have caused some incompatibility with HDCP and it was something I never considered, hopefully by sharing this it may help someone else!