Sliding contact might not work using linear static analysis. In linear static analysis, the contact status does not change, does not slide and the contact stiffness is constant throughout.
It is advisable to equivalence the sheet panels to the core instead of using the freeze contact.
The load and consequently displacements are so high it can be solved more efficiently in Radioss. Given the loads and BCs are symmetric you could reduce the model to a quarter for computational efficiency.
I have set up your model with imposed displacement of 10mm using NLSTAT analysis.