It seems the resolution DOES lie in that Fedora thread. This is the critical part:

Found it. gdk-pixbuf2 thinks it can't load SVG images, due to a stale /usr/lib64/gdk-pixbuf-2.0/2.10.0/loaders.cache.

The gdk-pixbuf2 and gdk-pixbuf2-modules packages are getting pulled in earlier in these installs than librsvg2, and the latter is not causing the file triggers from gdk-pixbuf2 to run, thus the stale cache. Forcibly reinstalling gdk-pixbuf2 afterward corrects this.

SLED did not have a package installed called gdk-pixbuf2 so I forced YaST to reinstall anything matching the pattern gdk-pix. This regenerated the cache file /usr/lib64/gdk-pixbuf-2.0/2.10.0/loaders.cache and the issue with logging in and unlocking the screen seems to have gone away on my Z440. I will try it it on the Z640 and Z840 this afternoon and report my findings.