When the SST turbulence model, or its variant with the transition modification, is used for cases with heat transfer, and the Reynolds number of the flow becomes so small that the flow is really laminar, then the discretisation of the energy equation at walls can lead to slightly incorrect temperature fields.
This is caused by the wall function in the heat equation not operating optimally in the laminar limit. Of course, the models are not said to work in this limit.
Calculate the flow with the Turbulence Model set to 'Laminar'.
ANSYS CFX Release 12.0.1. The fix is a change to the documentation, which now describes the limitations of the model