SEKN

Hi All. Does anyone have any insight as to why some of my files open as only a grey shadow in Cura?. The software seems to know the model parameters, because it will slice it, but nothing appears in any view aside from the shadow at the base layer, and nothing prints. Just confused as this happens maybe 5% of the time. I've attempted to go back trough several different software packages to adjust, but thus far no solution. Any thoughts? Please and thank you. Cheers!