I don’t know what’s causing it but if I insert a file and put the “object” on a layer and locks that layer then the objects are hidden.
Rhino automatically puts the inserted file on the active layer and I usually move them to a “0” layer (autocad style) to handle them. But if I lock that “0” layer then they disappear. Here I have done that with a mesh from a photogrammetry. If I lock the layerstructure of the file then it is not hidden, just locked though.