This may be caused by an issue fixed in 4.9. If you check the AndroidManifest.xml generated in your project’s Intermediate/Android/APK directory after packaging you will see an android:configChanges line; it should be:
android:configChanges="screenSize|orientation|keyboardHidden"
This can be fixed in UEDeployAndroid.cs in the GenerateManifest function or you can try the 4.9 preview 2.