If an app stops working properly, there are three things to try to remedy the problem. Here is a video that walks through all three.
If Apps are crashing: We have found that some apps need access to the camera and other ipad hardware, and if this access is turned off the app may crash. If this happens, go to Settings, and in the menu on the left scroll down and look for that app. Then check the sliders to see what permissions are on or off and try changing them.