OK, so I've ALWAYS (since AS14, 2007) had issues with applying colors/textures/etc in the 3D views. No matter how carefully I place the cursor, the color/texture/whatever often gets applied to something other than what I placed it on, usually something in the same line-of-sight, but behind or in front of the object I'm trying to paint.
AS20 has the same issue, especially in the animated walk-through. However, I've discovered that the overhead "room view" in 3D is almost 100% accurate. Which solves 99% of the problem (still a pain trying to get a custom toekick on a cabinet, or crown molding, but whatever, I can live with it.
What isn't acceptable is the "Smartwand" menu that pops up, even when I have Smartwand disabled. If I've got a relatively simple design, the menu isn't a problem - it lets me make a selection as to how the color should be applied (as designed, I'm sure).
But if I have an even mildly complicated design, or if I've put in a lot of 3D furnishings, cabinetry, etc., then that menu just pops up and instantly disappears, without applying the color to anything.
FWIW, I'm running AS20 on an Intel Corei5, with 16gigs of memory, Win10-64, and my OS on an SSD. I've yet to find a program that stumps this machine, but maybe AS20 is it?