This issue started happening since the BalanceRigidityEnabled setting was released to the GroundController.
Normal controller behavior, as to what ControllerService does; make the humanoid get up.
The humanoid attempts to get up, but not enough force is applied, even when BalanceRigidityEnabled is set to true. Even disabling the setting and cranking up the MaxForce does not work. What actually happens is the humanoid rig sinks into the ground by 0.1 studs when it is supposed to be getting up.