My ROG5 is doing fine, it's like using cheat while playing games like CODM or PUBG. Maybe the game is not optimized/memory leak, or it can be the weather in your country? disclaimer: I am a game developer, so I know about game optimization. We can't blame the devices totally if we create a trash game. Especially on a mobile phone, if you run a lot of apps in the background it can cause lags problems too. That's why ROG has a game genie & armoury crate to optimize the device and tune the performance.
Hi hp9976802431, I do play on ROG Phone 5. Can you share your gameplay and FPS if you see a drop in FPS. Also, what graphics settings and armory crate you use if any. Confirm your phone's software version as well.