Why only some tpk's show thumbnail in basemap window on windows 10 ArcGIS Explorer

[rzufelt]

I have sideloaded a mmpk (for operational layers) and some tpk's (for basemap imagery) onto windows 10 Desktop version of Explorer  for offline use. 

For some reason, one of the basemaps will show a thumbnail image, while the others do not. 

Any idea as how to get the preview/thumbnail for ALL tpk's that are sideloaded onto the unit?

Thanks,

R_