ANSYS has historically had a problem changing a 3D model into a 2D model.  I have posted many times that if someone in Workbench forgot to change the Geometry cell from 3D to 2D before they opened Mechanical and started building a model, that they had to abandon the work that was done in that model and start with a fresh model.

That means starting with a new analysis system such as Static Structural and pulling the geometry into that system opening the Properties tab in Workbench and setting the Ansys Type to 2D before opening the Model cell.

You may have changed a 3D property to 2D on an existing model and suffered defects in the computation because of that.  Ansys should do more to protect users from this defect.