You can change Quality from Low to Ultra! And if you are playing on server and there are a lot of people your FPS will decrase! And If you are playing on bigger map that may cause lag! And maybye your PC/Android is to bad for playing this game! :)
Same is happening to me but I was getting around 200 FPS and now i get around 20. I have restructured my settings to maximize the FPS but that doesn’t work. Also the dead bodies do not disappear anymore. When the bodies accumulate ( 100-200) The game becomes unplayable it is so choppy. And if CS wont run on my computer then something is wrong with the game.
Edit: Yup, just checked again on the latest version with High-Quality. Constant 60 FPS. And my computer isn’t exactly a gaming rig, either. Try setting Low Quality and turning off all settings, if it still runs bad my only guess is something is wrong with your computer.