By default, templates only contain references to the fills used for the style (You REALLY don't want to have them all listed, trust me :)), so that means that drawing tools not made for the current map style will show up using the currently selected fill (see your status bar), instead of the actual fill used by that tool in it's native environment. (Your current map seems to be the Ancient Tombs style)

There's more information in this FAQ topic, including how to import the fills to the current template:

Not for lines. Polygons gets a hollow middle whenever the line width is greater than 0, but lines will be solid all the way, unless you use the "hollow" fill style (You're not, since your rivers are using a bitmap fill) OR you have an Edge, fade inner effect on the rivers, where the inner opacity is set to be lower than the outer one.

Looking at your drawing, you do have an edge fade inner which is way wider than your rivers which is also the partial cause of your rivers being very difficult to see. I didn't notice that immediately when I looked at the map earlier because I worked with effects off to see it without the glow. You can try changing the width of this effect to something like 0.2 and see if that works for you.

Is this for any entity in the map, or is there a specific entity that crashes each time?

Can you share the .fcw with us?

These maps are now in the atlas. Thanks @Ricko Hasche for another excellent contribution.

Note that the Adill, Reefs and Uldir was wrongly scaled, they were about twice as large as the corresponding area on the parent map, so I re-scaled them and edited the scale bars.

It depends what you are going for. To create a top-down overview, any city style should suffice, you'll probably be mostly using the house tool to create your own shapes rather than using finished building symbols.

If you're looking to map the interior, dungeon styles will allow you to do that. I think you're probably be best off with a regular dungeon style, the Castles add-on will probably not give you too much for a magic scool, other than perhaps some castle drawing techniques, but in general, you'll probably enjoy a modern bitmap based artwork dungeon style more.

If you are after the perspective views, then Castles may help you a bit, but it is probably better to start out with Perspectives 3 instead. But a perspective view of such a building is going to be a complex task, so not a good starting point for an inexperienced user.