Hi there, Go to Settings, then Advanced features, then S Pen, then Air actions, then tap the more options icon, and finally Reset S Pen,
Check for third party magnetic covers that might interfere with your s pen, try to turn power saving mode, if nothing helps try to do wipe cache partition
Turn off your phone, connect to PC, macbook etc then press and hold volumeup and power button until samsung logo appears then quickly release power button and keep holding on volume up until boot menu appears then with volume down button navigate to wipe cache partition press power button and restart your phone.
