The newest version should have some of this fixed already by using a different folding piece with a tighter fit. Rule of thumb: if you have a hard time pulling it out it is fine.
This video shows what can possibly cause a wobble of the handlebar stem and folding mechanism.
I fixed the wobble of the upper bearing in its recess/hole with a piece of a plastic bag (0,1 mm thick plastic). Didn't work with a piece of aluminium (0,5mm thick) as I intended in the video because it was too stiff.
In the comments someone advised to fix the moving bearing with bearing glue, Loctite 638 should be suitable.
Wobble of my folding piece bottom inside the steering Tube was fixed by making it thicker with a few wrappings of cling foil (not kidding, it was the only thing i maneged to fit in AND it works).