Yeah, I know it was technically a GRUB issue, but I haven't found the active GRUB forums; I figured since it's causing an issue booting into KaOS, here would be my best bet; thanks for your patience.
So, yeah, I fugured "update-grub" should just fix this sort of thing (and apparently most of the internet thinks so too, since I couldn't find much on fixing broken GRUB2 entries). But it just wasn't. And I'm pretty sure that "init=" line was a desperate fix attempt I added after it was broken.
Fortunately I found that for some reason the GRUB auto-configuration script was setting the UUIDs for all entries to the UUID of the Ubuntu partition, instead of the correct partition for the OS. I couldn't figure out how to fix the script, but there was a custom entry i could edit, and replacing the UUID in that entry made it bootable.
Then I had to bump that entry up above the default one, because I guess the "saved" OS entry for rebooting into the previously running OS does not differentiate down to the specific entry, but grabs the first entry for the matching OS?
Anyway, it's a little kludgy and there is probably a more elegant fix (or maybe just a complete GRUB re-install that would be cleaner, but I can now boot into KaOS again, and both OSes will properly reboot into themselves without interference. So I guess I can't ask for much more than that...
Thanks again, both of you!