Model may look OK in DesignModeler (DM) but not in Mechanical. This is because Share topology is defined in multibody parts in DM. When transferring the parts, DM does Boolean operations to connect the bodies so that a conformal mesh can be created on these multibody parts. If there are penetration or gaps between bodies, this could cause problems with the shared topology Boolean operation and may result in incorrect geometry when transferred to Mechanical.
A good way to prevent it is to run a interference detection in DM. Interference detection in DM is a beta option. So from WB project page, go to Tools -> Options -> Appearance and turn on Beta. In DM, go to Tools -> Analysis Tools -> Interference detection (beta) . One can hide all other bodies and check only the suspicious bodies. If any issue are found, it should be fixed before transferring model to Mechanical.