I have this problem with ATV+ all the time. I'm running the app on a DirecTV Stream box. It's the only app that does this. All the other apps run fine all the time.. it's apparently a software glitch, probably a Timeout value that's too tight. I have 500mbps Internet, routonely get 600+mbps download speeds, and only two streaming boxes.
Retrying a couple of times usually works. If not, I switch to Prime or Netflix or Paramount+ or....
It's Apple. They're software, when it sucks, sucks deeply.