Second of all, have you tried factory reseting after the one ui 3.1 update?
Here is an example so you will know:
Go to settings > about phone > locate the model number and send it here.
Please go to this website and try the troubleshooting steps.
If it has not fixed your issue then book a appointment with samsung in your nearest service centre and ask them to check the problem.
The issue might be fixed by a firmware reinstall.
Backup your device if samsung says so.
we extremely apologize for the inconvenience that you are facing
kindly note that we always recommend our customers to perform a factory reset after the updates , but make sure to back up your phone's data before doing that
and if the issue persist then we recommend you to refer to the nearest authorized service center in your country