I've had the first issue with my Chinese engraver while experimenting to carve in wood.
What you can see in the picture is the result of pretty strong vibrations that rattled the linear bearings out of the spindle holder. While it is good to see that there's two on each rod ;-), this definitely shouldn't happen.
I am thinking about how to fix that. Perhaps it's possible to add a few grub screws from the side to hold the bearings? And I might have to reduce vibrations too - less deep cuts and slower feed rates might help.