Sometimes apps just get a little flaky, for lack of a better word, so the best step to take here is to close the app completely and then relaunch it. From the home screen do the four finger swipe up or double press the home button to reveal your multi task bar. These are all the apps that you have opened at one time. Long press the app until it jiggles and a red minus sign will appear above it. Press the minus sign, this will close the app, not delete it. It's also a good idea to close all these apps, as it helps the iPad run smoothly. Let us know how you go.