Decided to start posting a video tutorial series intended for beginners. The first few videos are now up and can be found in my playlist here:

I don't know the exact historical reasons, but I think you are onto the right answer with regards to paper sizes. Printing was much more important back when these were defined than today. And if you compare it to letter size, the aspect ratio matches better, and I am sure as Sue pointed out that having nice round numbers made more sense, so it does look like the numbers where picked to be a good fit for both monitor and paper as the prime concern

Of course, with the modern new map wizard, most templates allow you to pick values at any aspect ratio anyway.

Sorry about your job. Hope this situation normalizes soon so people can get back to their jobs, or at least have an easier time finding a new one when not everyone is trying to hunt in the same limited pool.

At least the time isn't wasted when you spend it mapping :)

If it only happens when the effects are on, it is probably one of the effects on that sheet that has to large a size.

If you can't spot the guilty one immediately, try disabling the effects on the sheet one by one.

And also make sure your floors are on the sheet you believe they are, you can check this with the Info -> List command.

Looking nice, but have you considered some kind of coastline effects on your map, there is a very sudden jump between land and sea, nothing that provides a transition. Often a simple outline or glow is enough.