Game has inconsistent frame rates

I'm playing on my Iphone 6 and the game suffers massively from slowdown. Game would play at full speed for 30 seconds and then suffer from a massive slowdown. It is unplayable at that point. It will go back up to speed 50 percent of the time. This device still has to option to change graphics so that means this device is still pretty well supported.

My Kindle Fire hd 8 has no option to change graphics (meaning its low end) yet it still plays the game at full speed. No problems at all last season for my Iphone 6.