Flow around cylinder gives poor results on unstructured meshes in Code_Saturne 9.1

We are testing the standard flow around cylinder case with Code_Saturne 9.1.

For structured meshes, the case works correctly in Code_Saturne 9.1.

However, with unstructured meshes, we could not obtain reasonable results. We tested both 2D/quasi-2D and 3D unstructured meshes, and also tested Reynolds numbers Re=200 and Re≈3900.

Observed behavior in Code_Saturne:

- No clear vortex shedding / Karman vortex street
- Poor wake field
- Abnormal velocity or pressure distribution near the outlet
- Outlet backflow messages such as `Incoming flow detained ... outlet faces`

For comparison, we ran the same meshes and the same Reynolds numbers in OpenFOAM, and the results were normal, with the expected wake/vortex behavior.

So the issue seems specific to Code_Saturne with unstructured meshes for the cylinder wake case.

Could you please advise whether this is a known limitation, a recommended setup issue, or a possible bug? Are there recommended settings for unstructured meshes in this case, especially for outlet boundary conditions, gradient reconstruction, or turbulence modeling?