why does system shut down after staying on 1 channel for a few hours?
You need to turn off Power Save Mode in Settings. Here is a great video that will walk you through the steps:
No, the TV set and converter both stay awake. Watch the video again. And nobody mentioned anything about a Roku device except @spongebob.
doesn't it still turn off after 4 hours even with that setting off. Especially the roku
If Power Save Mode is Off, the cable box should stay on after four hours of inactivity. Do not know how a Roku would effect this. As a Roku is third-party hardware there is no guarantee that it will configure with the box functions.
We can only assist with equipment and features provided by Spectrum. Other company hardware and configurations, we can only give a "best guess." This is because these products are not supported by Spectrum.