I have a weird problem using Vuforia (8.3.8 have to stick to this version) with Unity (2019.2) on Android. My app is forced into portrait mode. If I turn the device to landscape mode and open another app (because I'm sharing the content from the vuforia app), upon returning to the app, still on landscape mode, the AR content is rotated, not matching the position it had. The main AR camera is rotated around the Y axes by an angle, most of the time 90 degrees.
I have seen old posts from similar problems related to landscape mode messing up camera rotations, but all the solutions are related to old Vuforia versions and deprecated functionalities.