I've been noticing and increasing number of issues with physbones over the past couple of months.
1.
Immobile used to work with Gravity, but now bones with gravity always shake violently while the avatar is moving quickly, completely ignoring immobile.
Example:
avtr_ba3daad5-0c64-4fb4-8593-38265acd9ad3 avatar uses that to determine the up vector for the cat, walking around causes the cat to jump around, it never used to in older versions.
2.
Physbones resting on or inside colliders vibrate, sometimes even to the point where they seem to struggle to stay inside inside-out colliders. This used to be stable with no vibration. In minor cases this can sometimes be mitigated with "physbones as spheres", but it never used to be necessary.
Example:
avtr_04a9d322-e228-4934-93b1-6e20b62cfded The boxing gloves on this avatar are long physbones with squish that are held back by inside-out colliders, they now vibrate violently at all times, they used to stay calmly in place.