Though you used Shared Topology, there may be a piece of geometry that is not connected. A good way to find that piece is in Workbench, drag a Modal analysis out and drop it on the Model cell of your Static Structural model. In Mechanical, drag the Remote Displacement that supports the structure and drop it under the Modal analysis. Under Analysis Settings, increase the Number of Modes to find to 12. Solve, then look at the first 6 modes. If some modes are nearly zero, there is a part that is not connected. In the Details window, the part with the maximum displacement is the loose part. It helps if the geometry has been named in a way that makes it easy to identify. If not, you can see it by animating the displacement. Turn up the Result deformation scale factor until you see the part moving into view.
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