It could be the transfer of coordinate system from 3DSMax to UE, either from export settings and/or import settings. 3DSMax has a different coordinates system than UE, so try looking that up first. By default, what direction (or axis) does the camera face in 3DSMax, and how is the finished model oriented in 3D space in 3DSMax? For the scene, is the front of the round platform with the seat on it facing down the +X, -X, +Y, -Y, +Z, or -Z axis? Same for Unreal when imported, what axis is the front of the platform facing after import and before modifying its transform (location, rotation, size)?
There’s an option in the Unreal’s import dialog to change it to forward-facing x-axis. Depending on the axis it’s facing in 3DSMax upon export, this setting would need to be enabled or remain disabled. This aspect of export / import can change the lighting, texturing, and other facets of a model / scene because the data for lighting and such is derived from the coordinate system and used to build it. If they’re not the same in the two programs, it could easily result in weird problems such as the mirroring of the shadow.
Another thing is, why is the whole shadow not there? It has the middle bar that goes from side of the circle base to the other, but doesn’t have the other center bar that goes from the middle bar to the edge of the circle base.