I have seen this now 3 times today across 2 different devices. Auto-playing a daily quest, let it go for a bit then the screen dims and I can faintly make out its still on the questing screen, not paused, just not doing anything. I have to close the game and reopen to resolve.
This is not the OS dimming things to save battery its 100% an in-game issues. Add this issue to
https://forums.playcontestofchampions.com/en/discussion/305822/seeing-way-more-game-hangs-spinning-wheel-and-network-hanging-signs#latest and I would say the latest game updates are the issue......