Was having problems where during Acorn TV playback, I would get kicked out to Roku-Home.
I tried everything Acorn TS provided, most of which were already attempted, yet still not solved. Both TV's are Samsung.
This same Doc Martin issue was also happening on another TV with a different Roku device. I changed the setting in Roku, under Advanced Display Settings, from HDR 4K from 4:2:0 to 4:2:2. This fixed the issue on this unit.
The main TV was already set at 4:2:2 but had HDR 10. The fix on this unit was to change the Roku settings under Display Type from Auto 4K HDR 10 @60fps to 4K HDR 60 fps and voila!