Ouch Baja
so sorry to hear that! I can't unsee in my head what you lost!
Steve, I think the combination of uppotting with more than the needed fertilizer could be the culprit. This happened on some of my desert rose seedlings and they literally got amputated. If there are no black rot, then it is likely not a fungus. The good thing about aloes per my experience (which is limited) is even when I accidentally pull them without roots; I just put them an inch on top of a media and they develop roots.