Lag issues on the IPhone 6 (iOS 11.3)

My iPhone 6 was running my worlds with no lag on 1.2.11 but when I updated it to 1.2.13 or newer, it would be smooth but then it would drop frames rate and become smooth once again. This happens every 3 seconds and I also tried creating a new world and this would happen once again, making it kinda unusable