The app keep getting slower when play long time. (There is video)

Hi everybody, I’m user from THAILAND.
I have some problem after I installed my .apk file, When I play the app it’s keep getting slower, I tried left from app and in again the app is normal not slow untill I play long time,
I think issue isn’t from my phone,This app is turn you numberal base to base 10.

Problem video:

My apk link :

I’ve noticed similar behavior. Not sure what’s causing it though.