The Android Studio 3.1.2 bug-fix update is available in the stable release channel.
This update fixes several bugs and improves the speed of lint checking in some scenarios. For a list of fixes in this update, see the Android Studio 3.1.2 release notes.
If you already have Android Studio installed, you can get the update by clicking Help > Check for updates (Android Studio > Check for updates on Mac). Otherwise, you can download it here.