It appears that the problem was indeed related to the power supply.
I bought a 24V @ 5A PSU before the holidays, and yesterday I finally got a chance to try it. I can now complete a print at 50nm, which was not possible before.
I still have an issue with certain areas of the print surface. I printed a few things, and for some reason, in some ares of the platform, the print fails consistently (near dead center of the platform, and in the center, near the front). Other areas are fine. The failure is partial (just a small area of the total print) that is mangled or missing), but when I print 100nm in that area, it’s fine.
I’ll have to try a few more things, but suffice it to say, the main issue was solved with the correct voltage PSU.