Model Target Tracking works on Android and Editor but not in iOS

Hi Vuforia Team, 

we have an really annoying problem. We tried the model target tracking now with different model targets. All of them worked perfectly on Android (Pixel 2) and not bad in the Unity Editor (Platform iOS and Android). But it will not work on iOS (Testet with iPhone 7 and iPad Pro 10.5). We tried it with nearly all Unity Version which should work with model targets (2017.3.0;2017.3.1; and different patched versions of them and different Unity 2018 beta version) Everything looks good. Dataset is loaded die guide view is also the right one. On time it tracked one of the model target really good on iOS (for a long time -> did not looked like a false positive) but before that we rotate the iPhone 7 several times and suddenly it worked perfect. After that it never worked again. We get just one related errors (error is:

CameraDevice::getCameraCalibration(): Failed to get camera calibration because the camera is not initialized.)

and it even logs in xCode that the right model target is loaded and activated (no other targets inside). We even tried the native version of your SDK for iOS and we have the same problem there.

So this is really annoying cause we think we should have done everything right (same project works perfectly in Android and Editor). We also tried different model targets. So can you maybe help us with our problem? There must be one special setting we forgot for iOS or something similar cause it works on Android. Is there maybe a version of your SDK which you can recommend working with iOS and Model Targets?

Thanks for your help.