Fusion 360 step. file becomes hollowed out while after exported into comsol

[MattL48WM]

Hi, was wondering if anyone's encountered this. The bodies appear to be completely solid in Fusion, but once exported into COMSOL, the bodies all appear to be hollowed out

[TrippyLighting]

You may want to share a bit more information about CONMSOL. I am not familiar with that software.