This is a special case that happens with symbols. The thing that happens is that all symbols have their definition on the SYMBOL DEFINITION layer. And if you hide the definition, the symbol disappears. So symbols will always be hidden either if you hide the layer it is on, OR if you hide the SYMBOL DEFINITION layer. So if you are trying to get to an entity by hiding all the other layers, make sure you leave SYMBOL DEFINITION still visible.

As JimP says though, it shouldn't be on the MERGE layer, so use change properties on it to put it somewhere else.

They only affect the current CC3+ session. The default at launch should be smart symbols on, but they won't reset by simply loading a new map.

Note that you can also find the same setting in the symbol parameters dialog (the one you get when right clicking with a symbol on the cursor)

Disabling smart symbols disables everything that is smart about symbols, like connecting symbols, control points, random selections from the catalog, etc. Basically, they lose all behavior and gives the user full control.

Also note that if Smart Symbols are disabled (Options button on top of symbol catalog) connecting symbols won't connect, but just behave as individual symbols.

Not sure exactly what you are referring to here. Polygons can be mirrored, but only along a straight line.

You may be thinking about using an offset, but if so, you'll need to draw one line, then making an offset from it, and then join them together with Combine Paths and Close Poly to create an actual polygon, and not just a series of lines.

Jerry was a dedicated mapper, and loved making maps for the atlas. He was a valuable community member that will be missed.

All his atlas maps can be found from the search page by searching for Jerry Thiel as the author.