You can get some info about the problem on this post. https://developer.vuforia.com/forum/general-discussion/improving-tracking-tracked-image-moves-0
Summarizing it. Initially we were running with pointcloud, because the slam was pretty useful since they’re pretty big objects (Scenes of 5x5m aproximately). After this change of requirements we’ve tried UCS and Vuforia (with extended tracking), we've run tests with single trackers (A3ish) and multiple planar trackers between others, . And while it improved a lot it’s not good enough for our client.
So basically we need someone with enough vuforia expertise to solve these problems.