Refer to figure.
The Bell rotor stabilizer bar positioned at 90° to the rotor blades plays a crucial role in certain helicopter rotor systems, enhancing stability and control.

In the initial state, when the helicopter is stationary in a hover, both the rotor and the stabilizer bar align perfectly and remain parallel. During this phase, no input is directed to the mixing unit, ensuring the helicopter's stability.

However, when an external force, such as a gust of wind, displaces the rotor from its parallel position, the rotor disc starts to flap, resulting in tilting or movement relative to the helicopter's body. In the example you provided, the rotor disc flaps backward due to the wind gust.

The stabilizer bar possesses a substantial amount of gyroscopic rigidity due to its mass and synchronized rotation with the rotor. This inherent gyroscopic characteristic enables the stabilizer bar to resist changes in its orientation. Therefore, the stabiliser bar increases the pitch stability.

When the stabilizer bar and rotor blades are no longer parallel, the mixing unit comes into action. In the specific scenario you described, where the rotor has shifted while the stabilizer bar remains in place, the parallel alignment is disrupted, prompting the mixing unit to respond.

The mixing unit's role is to adjust the pitch of the rotor blades in response to the misalignment between the stabilizer bar and rotor. For example, if the rotor has flapped backward due to the wind gust, the mixing unit will modify the pitch of the rotor blades to counteract this movement and restore stability.