I have been having the same issue with YouTube and Emby, the only two apps I use 90% of the time on my Roku 1. It started a few weeks ago after the latest update.
Both apps return to the home screen after 30 minutes of playing a video. It doesn't happen with videos shorter than 30 minutes.
Since it happens at the same time length every time, it seems to be related to some sort of timer in the Roku, perhaps thinking there has been no activity for 30 minutes so it exits to home screen.
I've read all the old posts about similar issues and can see that this is a problem that has come up with various apps in the past. None of the past solutions have worked for me.
Try changing screensavers.. might be a buggy screensaver.
I use three apps on my Roku almost daily. Roku Media Player is for watching media from my home server via DLNA, then YouTube and Prime Video. With all three I often watch media that lasts over 30 minutes without getting kicked back to the home page. While it's rare that I've watched a YouTube live stream that lasts that long, I have watched some SpaceX launches that lasted over an hour. I don't think there's anything within the Roku firmware that is causing a return to the home page after 30 minutes. But what's causing your issues, I can't venture a clue. Hopefully tomorrow when the Roku forum admins are here again they can do some investigation for you.