Unstable positional device tracking on iOS

Vuforia SDK Version: 7.5.20 - Description with steps to reproduce: Hi all, We are porting a mobile application from Unity 5.6.X to Unity 2018.2.7f1, so we are also migrating from Vuforia Legacy to the new Vuforia 7.5.20. We already followed all the migration steps suggested in the docs and we have the new version up and running. We have a VuMark dataset with string IDs (5 characters long), and the VuMarks are very small (around 2 cm wide). We have an issue on iOS regarding the Positional Device Tracking on recent iPhone devices (iPhone 6 and laters). When the app recognises the VuMark and the user starts to move around, the Positional Device Tracking moves my 3D model instead of keeping its position. We do not have this issue on Android, where the positional device tracking works as expected. We also do not have this issue on iPhone 5, maybe because it is not an AR Kit device? Does someone have the same issue? Does someone have already solved it? We cannot remove positional device tracking since the user experience will be very poor without it. Any help will be appreciated. Thanks. - Development OS (Mac OS X, Windows, Linux): Mac OS X - Mobile OS and Version: iOS 12 - Mobile Device Manufacturer and Model name: iPhone 6 and laters - Do the Vuforia Sample Applications show the same behavior?: If I add my VuMark dataset to the Unity Vuforia Core Samples VuMark project the application shows the same behaviour. I was not able to reproduce the behaviour with the provided VuMark dataset.