Wipe your cache partition. >Power off your device. >Press and hold, Volume Up + Bixby + Power button to boot your phone into the recovery mode. >Press volume keys to navigate and power button to select. >Select 'Wipe cache partition' and confirm. >Select 'reboot'. Normally this will not effect any personal data or settings.
If the issue still persists even after wiping the cache, then check whether it happens in 'safe mode' also. If not, you can make sure that the issue is caused by any third party apps.
