I've been using Channels for a few years now in Australia on digital TV on an AppleTV (3) 64Gb A1625 TvOS 14.2 with a HD Homerun quad tuner.
I generally only ever watch the one channel, and usually only in the morning. When I wake up I want to shift back to the nearest 30 minutes so I can get the news headlines. e.g. if it's 7:40, I shift back to 7:30am. I'll often skip back to the current time once I've seen the headlines but not always. When I'm done I turn off the TV but leave the Apple TV on, with the channel active in Channels.
Everything worked well until a few months ago when I was unable to time shift if the channel had been active for a while (and hence had a big buffer) - for instance if I left it on the channel for few days without exiting/changing channels to reset the buffer. I don't know exactly how long is too long for the buffer.
When it occurs, for instance from me pausing in preparation for the timeshift, the timeshift indicator will move to the far left of the timeline rather than the far right (current time). I know it's not going to work from there. If I then scrub to any point on the timeline the screen will be frozen on the frame and won't play. The only way to "fix" it is to exit out or change the channel - and unfortunately losing the entire buffer.
I know the AppleTV is old and the TvOS is EOL, probably meaning no updates can occur anyway. I do wonder if the same problem is occuring on "supported" Apple TVs as well though, before I think about upgrading.
The reality is I only really want a short buffer - maybe a few hours, not several days worth. I wonder if creating a configurable "max buffer" might help fix the problem?
LMK if I can offer any more details.