That is a frustrating issue, and I wish Apple would come up with a fix! But there is a workaround.
Try this…Close the App Store completely from the app switcher window by double clicking the Home button and swiping up the App Store preview pane until it disappears from the screen. You may have to look for the App Store pane by scrawling to the left.
Then sign out of the iTunes Store (in Settings).
Then do a forced restart. Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears.
Then sign back into the iTunes Store.
Hope this helps!