2 of my games are freezing and greying out

When I play 2 of my games (Top Gear Race The Stig and Subway Surfers) the games freeze and grey out. Sometimes they grey out as soon as they have passed the loading screen, and other times I play the game once (or a few times) before the issue happens. I have checked the App Store reviews and not found anyone who has this problem. I have also backed up and reset the iPad, and uninstalled and reinstalled both apps. None of these have sorted the problems out. I am open to suggestions to solve this problem.