Oh, good to know you're a Samsung user. Try this out :D
It's an official tool which allows to control graphic settings for any apps in game category. Default settings of 75% resolution and 60 FPS works well on lag reduction.
If lag still exists and you don't care about graphics quality, 50-60% resolution could help.
Read this. Also some phones touchscreen acts weird if you are touching your screen while playing (for example your fingers are resting on the edges).
That's weird, perhaps you accidentally deleted a file? If it doesn't work, I would try uninstalling the game completely, and downloading everything again fully and try the renaming method after the tutorial. I would say if that doesn't work, then you can download this app to rename the files instead. People from discord confirmed it works. https://play.google.com/store/apps/details?id=com.estrongs.android.pop&hl=en