Does this "ringing" mean that the encoder goes one or several full step back and forth at a speed higher than during steady rotation, or is the "ringing" a consequence of oscillations of the encoder around one transition point?

One type of an encoder is a disc of alternating opague and clear fields read by a photocell. This disc acn be 2" (5cm) diameter and have 100s of transitions. Now visualize that the final stopping point is exactly where balck and clear meet. It will tale a minuscule movement (1/100 of a degreee) for the photocell to see the other field of the disc.

Just visualize any mechanical drive stopping there which gives a lot of up down reversals. I have seen them in the MegaHertz range.

Erik