Hello!
I know a lot of people have been having issues with freezing and slowdown. From what I've concluded it's to do with the refresh rate not restoring properly after its gone to it's screen off state!
Simplist method to fix this fast with minimal effort is to switch your refresh rate up or down
To have a more semi-permanent solution we will have to use a third party app called Galaxy Max Hz
I don't fully know the rules of the sub but you can find this app and it's details from an easy Google as you will have the install the APK
Once the app is installed follow the guide on getting setup and navigate to the bottom of the initial page labelled force lowest HZ this will make sure every time you turn the screen on the app will make the adjustment back to your set refresh rate.
This may take a bit of ADB knowledge to unlock but the app should guide you through how.
Any questions let me know