I got a successful build using BuildThirdParty.sh -b SDL2, but, unfortunately, that didn’t take care of the problem. Looking at the behavior more closely, what I’ve noticed is that if you go to a quad-pane view, you don’t even get the marquee - and the mouse will instantly jump to the center of the screen. If you toggle back to a single pane view in either front, top or side, the marquee returns, but the locational positon of the mouse/cursor jumps to the center of the screen, no matter where you click.
Thanks for the suggestion, RCL. Really appreciate you helping me with this.