Fps lowers significantly when tab back into game

I have come across a bug with my game whenever i tab out from it (ie press home button and dont close the app) doesnt matter which time in game when i come back to it the fps drops under 30 whereas under normal conditions it stays as a solid 60 using a smooth fps i am guessing its something to do with whenever the game is in the background the recources provided to it from the phone lowers but then why whenever its opened it doesnt go above 30 until i restart the game and also does anyone come across this before and have a solution or reccomendation. This game is also still in development and tests are performed by packaging the game and using a batch file to get it on the phone. Thanks in advance.