Update to iOS 12.1.4. This may solve the issue
iOS 12.1.4
iOS 12.1.4 provides important security updates and is recommended for all users.
For information on the security content of Apple software updates, please visit this website: https://support.apple.com/kb/HT201222
Apple security updates
This document lists security updates for Apple software.
About Apple security updates
For our customers' protection, Apple doesn't disclose, discuss, or confirm security issues until an investigation has occurred and patches or releases are available. This document lists recent releases.
For more information about security, see the Apple Product Security page.
Get the latest software updates from Apple
Keeping your software up to date is one of the most important things you can do to maintain your Apple product's security.
About iOS 12 Updates - Apple Support
https://support.apple.com/en-in/HT209084