I actually faced a similar issue before where the game started lagging badly after a few matches and the FPS would suddenly drop. In my case the problem happened when I installed Subway Surfer from an unsafe or random source. The files were not optimized and after a few games the performance became really unstable.
Later I found a better and more reliable source and after installing the game from there the gameplay became much smoother and the lag problem stopped. If you are facing the same issue, you can try downloading it from here and see if it works better for you:
https://subwaysurferapkhub.com
After installing from a proper source the game usually runs much smoother and you can enjoy better performance on your mobile or device.
