The mirrored reflections of avatars update poorly if the avatar, or at least some kind of a "visual bounding box", is not on the screen.

For your own avatar, it appears like unrigged attachments start moving intermittently and going out of sync, but rigged ones still behave normally. For other peoples' avatars, all body parts, rigged and unrigged, start stuttering equally or even fully stop.

At least keyframed in-world object motion is unaffected and updates smoothly, did not test direct script driven movement or physics objects.

A still image helps only so much to visualize, but my own avatar is on the right in the picture: note how the head and hat (unrigged parts) are completely out of sync with the hair (rigged), same for the green cube (should be on right hand, but is nowhere near).

A video clip of the effect, please ignore the unrelated stutter at the start caused by Gyazo behaving poorly: https://i.gyazo.com/8fc69b7565ee850bc52556074e4fd105.mp4

As I zoom in, the avatars' "visual bounds" go out of camera and the other avatar stops entirely (skeleton body is rigged, red cube head unrigged), and my avatar's unrigged parts as above go out of sync. The keyframed crystal movement in the back remains smooth despite being further away.