Thanks for the reply, but it turns out it isn’t so much a slicer issue, but a pebkac.
This turned out to be an onshape design problem of mine. When I extruded the numbers into the face of the icosahedron, creating the number part, it didn’t “delete” the part of the icosahedron that interfered with the extrusion.
Thus, when I exported it the icosahedron was literally that, without breaks for the number parts. While the prepare tab showed fine, the slicer chose to ignore the parts that were essentially buried within the icosahedron, even though they could be seen at the serface.
I ended up fixing this in onshape by using a boolian removal against the icosahedron using the numbers as “tools”, then keeping the tools. This essentially removed the shape of the numbers from the solid of the icosahedron.
lmk if that makes sense.