Physbones will jitter when Immobile Type is set to the "World" option while the Immobile strength is set to a high value (Especially when set to the maximum of 1). They will jitter even when the player is standing completely still, and the issue appears to get worse the further a player is away from the origin point (X=0 Z=0) of the world, though the issue is still present regardless of where the player is located. The issue is persistent on PC (both desktop and PCVR) and is present on the Quest platform too.