Why the drone is drifting in HIL?

I am running the
PX4 Autopilot in Hardware-in-the-Loop (HITL) Simulation with UAV Dynamics in Simulink
example，after the set-ups, I run the UAV_Dynamics_Autopilot_Communication model, the flying which should follow the waypoint is not act as I expected in QGC:

there are some warnings on the top and the drone was drifting after following the trajectory.
and a module called 6DOF Rigid body dynamics is in red:

except this two wierd things happen, everthing were fine. No Warning information from Simulink.
I am not sure the fact that 6DOF Rigid body dynamics is red is relative to the drifting, but they show up together makes me curious.
How can I fix the drifting? Why the module is in red?
Thanks for your answer.I am running the
PX4 Autopilot in Hardware-in-the-Loop (HITL) Simulation with UAV Dynamics in Simulink
example，after the set-ups, I run the UAV_Dynamics_Autopilot_Communication model, the flying which should follow the waypoint is not act as I expected in QGC:

there are some warnings on the top and the drone was drifting after following the trajectory.
and a module called 6DOF Rigid body dynamics is in red:

except this two wierd things happen, everthing were fine. No Warning information from Simulink.
I am not sure the fact that 6DOF Rigid body dynamics is red is relative to the drifting, but they show up together makes me curious.
How can I fix the drifting? Why the module is in red?
Thanks for your answer. I am running the
PX4 Autopilot in Hardware-in-the-Loop (HITL) Simulation with UAV Dynamics in Simulink
example，after the set-ups, I run the UAV_Dynamics_Autopilot_Communication model, the flying which should follow the waypoint is not act as I expected in QGC:

there are some warnings on the top and the drone was drifting after following the trajectory.
and a module called 6DOF Rigid body dynamics is in red:

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