That's quite a few apps resident in memory at once, and depending upon the total memory installed in your device, it can lead to unpredictable behavior. The memory we're talking about here is RAM, or application memory, not the 8 GB - 64 GB that you see when you check Usage in settings or the number that is printed on the back of your device .
If you wouldn't mind trying something, it would help us determine what might be causing the issue you're seeing. Please try the following procedures and let us know if the game starts acting more normally:
Launch Safari and tap the icon with the number of open pages (the one you indicated that showed six). On the next screen, tap the 'x' on each open page to close all Web pages (tabs) to free up memory, then press the Home button. Do the same for other browser applications you may be running.
Next, access the multi-task bar by double-tapping the Home button. Press and hold one of the icons until you see badges with a dash appear in the upper left corner of each icon. Tap the red badge for each application to close all of them. Each of those apps occupies a certain amount of RAM. Although they are not actually running and don't have a direct effect on device performance, the cumulative memory that they occupy can result in causing other apps to have problems due to low memory conditions.
Please let us know if this helps.