Extended Tracking - keep object alive even if handheld is moving fast

Hi!

I am building my first vuforia - unity applications for a customer.  Right now I am havin a minor issue: With Track Device Pose enabled, Tracking Mode Positional, Fusion Mode set to Optimize for Image Tagets and VUMarks the model on the handheld screen is destoyed if you move your handheld too fast. Right now I dont see the reason for that behaviour why it  should work like this. Can I change this? Is there a button I have not seen? Do I need to implement some coding?

Also some objects vibrate a bit if I go close to them. Is that normal? Can I change that too?

I tried to find articles about those topics but havent found any. The library haven't answered them as well and when I searched for 'Persistent Extended Tracking' all forum entries pointed to articles inside the library that dosn't exist animore.

Thanks!