Really it's the only Apple TV app that I regularly have issues with! Sometimes it opens to just a blank gray screen, sometimes you start a video and sits there waiting to start endlessly and doesn't play anything, sometimes it won't send the audio to connected Homepods for mysterious reasons, and even when it works it is so unbelievably slow.
The Nebula app also isn't great, but at least it functions, even if it too is slower that molasses in January.
I think I've once had it freeze and I had to restart the device - but when it is working it is quite snappy. I don't even think its the device - we upgraded from quite an old Apple TV model to a new one and it was equally usable on both.
The Nebula app also isn't great, but at least it functions, even if it too is slower that molasses in January.