we found a bug in Unity 2017.3 and upwards using Vuforia 7.x.
We reproduced it with new and clean Unity Projects, which only used Vuforia for Android and iOS and the Vuforia Examples.
1. Setup a new scene
2. Add Vuforia Camera
3. Add ImageTarget (for exampe Astronaut or Oxygen)
4. Start the playback mode
5. Scan the Target
6. Debug Log shows "Trackable xxx found"
7. Disable the VuforiaBehaviour while the target is being tracked
8. Log shows "StopVuforia" and "Trackable xxx lost"
9. Move the camera away from the target or hide the target, however, make it not visible for the camera
10. Enable the VuforiaBehaviour
11. Log shows "StartVuforia" and "Trackable xxx found" and immediately "Trackable xxx lost"
Point 11 does not happen always, but very often. And that´s the problem and bug. The target is not been seen, but is fired as tracked. And if this triggers something in your app, this is not desired to happen, when the camera is not pointed at the target at this moment.
The same setup done with Unity 2017.2 and Vuforia 6.5.x does not lead to this error. Here point 11 always finishes with "StartVuforia" only.
We reproduced this with Apps using different Unity/Vuforia Versions and with this "Vuforia Only Dummy Projects" like explained in this example. Unity Editor and Device.
Will there be a fix soon?
Martin from KIDS