In addition to what Sue is writing above, check for double walls. When I look at the screenshots you post, the door is clearly cutting something, otherwise there wouldn't be a white rectangle there. And the wall fill pattern in the second image is offset from the first one, indicating that there seem to be two walls on top of each other there. (The wall cutting functionality only cuts one entity)

I assume you are talking about the Annual Jon Roberts cities here?

I think it is just a color issue, the symbols in this style is quite simple, and mostly white, and the white symbols on the white background makes them invisible.

Note that you don't have to place them from the new map wizard, you can also access these symbols after starting the map by hitting the :ICON_DRAWING: button. (They'll be just as hard to see in the symbol catalog window though, unless you change the view window color from the View menu to something not white.)

1. When you hit the add-on buttons the program loads some defaults to ensure that things work sensibly. For example, if the overland filters were kept when you went to the DD3 add-on, all catalog buttons would just return empty results because the overland filters doesn't make sense in a dungeon setting. Unfortunately, this also means that the settings loaded with the map is lost. Generally, it is not adviceable to use these buttons in the middle of a map. If you wish to load symbols from a different add-on, use :ICON_CATALOG: instead, this allows you to load any catalog, not just the one provided by the defaults for whatever add-on you switch to. The easiest way to reload the correct settings is to just reload the current map, you don't need to restart the program. Simply save the map (if you have changes you wish to keep), then simply pick the map from the top of the recent file list in the File menu. This will reload the map, and reload the settings from it.
2. One way of making torn edges is to place a white polygon with some fractalized edges on top of everything. The white will cover up part of the map, appearing as a tear. Add some inside glow and perhaps some blur or similar to make it look more like a tear and not just a flat poly.

You don't need to start again. Just run the update installer (Update 27, 3.97 update) and let it take care of things.

No, not reinstall CC3+ itself, but the latest update (Currently update 27). The update fixes things not just with the core CC3+ install, but also updates files from the add-ons which is why it should always be installed after installing an update (or at the end if you install several in a row) even if you have installed it previously.