Using Unity 2018.2.5f1.
VuforiaConfiguration: tracking mode positional, optimize for Image target, track device pose ON.
Since we upgrated Vuforia to 7.5.26, we have a new serious issue on Android only, iOS still working as a charm.
It looks like the extended tracking sometime fall into a weird state after moving/rotating the mobile quickly. Instead of losing the tracking as usual, the 3d world slowly rotate and drift even if the mobile isn't moving a bit. At this point, I have to really make sure I lose the tracking and look at the image target closely to fix it. We do not have any code that would move/rotate the world like that.
I was about to downgrade to 7.2.24 but since Unity announced that they are upgrading to 7.5 themselves from ~2018.2.13, I don't know what to do. Our devs/QAs are reporting the issue and I can't give them any ETA.