Objects placed on ground plane drift on ARCore devices

This is with the ground plane demo and with our own implementation in Unity. 

• User places the astronaut on the ground.
• User can walk around the astronaut and walk towards her and she stays in place
• User puts down phone or turns away from the astronaut and causes it to lose tracking.(Losing tracking means that when the user attempts to look back at the building, it is no longer there.)
• The user looks back at the astronaut and now she no longer stays in place. She drifts as the user moves the view, cannot be walked around, sometimes drifts on her own. Behavior is largely similar to the mid-air demo. 
• This happens whether or not the user uses the reset button. Resetting does not fix the issue
• Restarting the app fixes the issue
• Switching to another app and then back again while the AR is running also sometimes fixes the issue. 
• This happens on ARCore devices (Samsung Galaxy S7) consistently. My QA team says it also occurs on non-ARCore S6 and ARCore S8
• Testing with iPhone with ARKit on another device in the same room has no problems
• Room is well-lit with a regular patterned floor. Happens in multiple different environments consistently however. 

Our team is interested in knowing if this is an issue other devs know how to correct. Or if it is a bug in Vuforia that they are planning to correct soon. The feature is being used in a game that we have to finish and if it isn't fixable we need to know asap so that we can use another AR SDK. The inability of the reset button to correct it makes it not feasible for distribution in our game. 

Thanks