I have this same issue. Mine will sometimes go for 45 mins before rebooting to the home screen. Doesn’t matter what app is being used. Swapped out the flex box with a new one, same issue. I have mine hard wired so not using WiFi. I guess you get what you pay for, it is free and Xfinity isn’t spending time fixing their issue.
I’ve been watching Premier League on Peacock, and the app is crashing about four or five times in a game. It says that it lost the internet connection, but the rest of the devices in my house have no problem. It happens in other apps as well - we watched a movie on Amazon Prime and same problem.
At this point, I only use Flex for the free Peacock subscription, and my Roku for everything else.