Yes I have the same problem. The Spectrum technician said the Roku signal was too strong and it takes over the TV. I wonder if there is another Roku that can pick up Amazon Prime but doesn't take over the TV.
Good evening I resolved my problem, as it happened I had a Panasonic DVD reader & its remote control combined DVD as well as TV. I had not used this remote for quite a while so I changed both batterie & then I could get control of the TV & choose between the TV (in may case HDMI 1 for the TV & HDMI 3 for the ROKU unit. I tried to change both way & it is working fine.