It's an advanced topic, not covered in the manual.

It's described in the help files accompanying the program, and also in the Tome if you own that.

Check out this article:

He's used the standard Mike Schley overland style (in a nice creative way), which comes with CC3+. The building on top is one of the monthly freebies.

I can't open your map right now, but check your sheet order. The behavior you describe is exactly what happens when the symbols go to a sheet that is hidden by something else, for example a landmass.

For performance reasons, when you place symbols, they will always appear on top of everything else, but once you change the view in any way, the view is recalculated, and everything goes into the correct position based on sheet order. The fact that the symbols disappear means that they are on a sheet behind something.

Also note that the Shaded Polygon command changes the fill style to whatever is currently selected. You can use :CC2KEEP: to set the current settings to match that of your poly before running the command. Or you can use the Shaded Polygon (Angle by Edge) command which doesn't do this, and at the same time figures out the correct angle for you.