i'm analysis thin disk & impeller now

I understand that U_θ and U_z allow radial deformation due to the centrifugal force acting on a rotating body, permit tangential (theta-direction) deformation relative to the edge of the bore center, and constrain displacement in the z-axis.

In this case, is it unnecessary to separately constrain the rigid-body rotations R_r and R_θ?
I would like to know the reason why.

Also, when the analysis is performed with only the U_θ and U_z constraints, there is no issue at low RPM, but at high RPM negative values appear.
What is the reason for obtaining negative values at high RPM? (1st picture)

Additionally, after applying only rotational constraints on R_r and R_θ and completing the analysis, the following error occurred.
Why is it not appropriate to run the analysis with these rotational constraints? (2nd picture)

Although the von Mises stress results were almost identical to those obtained using only the U_θ and U_z displacement constraints, the displacement results showed a difference of more than 10%.