Vuforia tracks without showing objects

I've asked this in the Vuforia forums with know answers...I'm developing using unity 2017.3.0f3 and a webcam. Occasionally (about once in every 10 times) I notice that vuforia starts tracking the cylinder target, but does not show it's child gameobjects in the scene. I've attached a screenshot of what this looks like in the editor. What would cause this? I have disabled extended tracking. I've taken a screenshot of when it starts tracking, it shows the camera but no gameobjects.