It's the snap setting. Snap and Cursor snap is on, but for some reason, no grid is selected. This basically causes everything to snap to 0,0 and nowhere else.

Right click the snap button in the lower right, and click on one of the existing snap grids in the list (or create a new one)

The change doesn't change anything in the actual map, just changes some parameters for how CC3+ does the rendering of it.

The setting is persistent in CC3+ until you close and reopen the program, so it will affect any maps you open in that instance of CC3+.

To always have it load for a particular map, you can put DELAYDRAWSYM 0 into the OnOpenMacro of the map file. (Obviously, this will keep it active for the lifetime of the instance and not just for that map)

CC3+ is mostly single-core, so it does benefit from higher clock speeds rather than many cores. Normally, I would recommend an Intel over that Ryzen 3600, but of course, with the new 5000 series just released and your motherboard being able to handle it, going that route is probably beneficial in the long run although the current Intel motherboards should be compatible with the next intel generation coming next year, which may (or may not) change things here.

I can't really comment anything about the release plans for CC4, other than it is not something that is right around the corner.

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.