Thanks for reporting this bug. It's a big deal for my workflow.
RE: The 12-Core. I've only been running v19 on it for about a week and a half so I haven't been able to flex all the muscle I expect it to have. Yes, the elevations with texture and shadows are faster, but by how much, I can't tell. Since I haven't been able to (repeatedly) achieve a successful sketch render with all the settings on, I can't fairly reply to this either. I have not tested the Maxon Engine, as Atlantis is still my familiar workflow. If you have a benchmark file or evaluation tool to compare times and speeds with, please contact me and I would be happy to post review.
I just loaded a LARGE file that I created in v17 and did a render test on both. Ironically, the shadows and transparency worked this time on this file using v19. Comparing the speeds to generate the exact same sketch render, I was surprised to see that the v17 render was 2 seconds faster.
Here are a few more observations regarding idiosyncrasies or bugs since I have your attention.
1 - When I have multiple sessions (projects) open in v19 on my Mac, when I close one of them, the dock icon still shows it being open with it's file name still activated with that small white banner across it. I have to quit the additional session to make remove the file name.
2 - If I close a project file while there are still "tabbed" render images left open in the viewport, the project file itself closes and saves, but I get a save dialogue asking me to save the "xxxxx.pln" file instead of the actual tabbed image file, i.e., "Picture #3". Its confusing and makes me second guess whether I successfully saved the .pln file and all the work I did in it. I guess I'm surprised that the actual CAD file will close before the images generated in a session.
(unnerved by updates since v.4.55)