After I manually add ARAnchors to an ARSession, I never see them updated in the didUpdate function. ARPlaneAnchor's update fine, but even when tracking jumps after what looks like loop closure/relocalization, my ARAnchors are static.
Do regular ARAnchors ever update their transform?
I do have update in the didUpdate function with ARKit 1.5 beta 2. I manually add ARAnchor at some location where the device go (using device position as anchor position). And then, when the device look at already seen area, I get the updates. But the position are very slightly updated (1-2 cm update).
I just posted another question linked to your question I guess : ARKit ArAnchor behavior