I have got it working now with help of this article: https://library.vuforia.com/content/vuforia-library/en/articles/Solution/arcore-with-vuforia.html

I am using core-1.4.0. The scale is now the same on Android and iOS. 

Hi,

I have the same issues; on iPhone (support Fusion with ARKit) everything is correctly scaled but on my Samsung S8 (no support ARCORE from Fusion only VIO) then the objects are 5-6 times smaller. When you move the phone sometimes there is some rescaling of objects. It looks like Vuforia groundplane without Fusion Providers (ARCore/ARkit) is not stable on scaling and positioning.

Greetings,

Mark

have you queried your app to see if its using VIO or ARcore under the hood? (Id recommend the vuforia sample scene for starters as it works fine)

its probably your environment/surfaces/lighting causing the problems

I can get reliable results on my S7 (which runs the inferior VIO fusion provider mode) if I point it as something like this,

https://appcircus.com/files/applications/qr_codes/acrossair-augmented-reality-browser.png

in perfect outdoor, cloudy day diffuse lighting

If I move indoors and point it at things like white shiny desks, it has trouble.

ARcore/kit use the IMU and Gyro on your phone in a tightly integrated way, so the results there will be better.

Tom