This a view of the Design library. All of these are .SLDBLK and were saved the same way into the same PDM directory and checked in, maybe by different people.
Make block > Save block. Why are the icons different?
you mention PDM, so maybe the ones showing just the icon and not the preview are ones you do not have a cached copy of?
That was it. I went to blocks directory in PDM, did a Get Latest, then went back to the drawing and did a refresh
of the design library and now I have
Retrieving data ...