Extended Tracking losing target issues

Hello,

I'm using Vuforia for extended tracking using an image target. On my image target there's an item that, when a button is pressed, moves around the environment. Sometimes, whenever the image target is lost, I can follow around the item without any issues, but sometimes (especially when the item is above me, or the phone is tilted over 45 degrees on the X-axis) the item starts to flicker and it then dissappears.

Is there any solution so that the extended tracking can be more accurate?

I'm using Unity 2018.2.0f and Vuforia 7.5.2.