We’ve found a workaround that goes like this. Open the blocks that are not showing, duplicate an edge or somehow draw a line or curve in the file. Save the file and update blocks if needed. You also have to move the block once back in the assembly. I use nudge to move it and move it right back. If you don’t do this, your shaded view will display the block as a wireframe.
In other words, if your inserted blocks have a line saved in the file, it will show normally.
Duplicating an edge works well. It’s there, it’s compact. and it doesn’t show up.