Hi @Ak3
Have you performed any recent software updates ?
Are your apps in the Playstore and Galaxy Store updated ?
To start troubleshooting this can you perhaps try the following generic troubleshooting guides.
- Https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.
- Https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/ turns off downloaded apps and themes etc which may highlight an app or theme that's causing conflict.
- Use the diagnostic tool in your Samsung Members App under the GetHelp section.
- As a very last resort back up and factory reset the phone.
- A Samsung Service Centre can help.
I wish you all the best. 
