The rapid spreading suggests sclerotinia rot. Do you see a white fuzzy growth on the bottom of the stem where the rot is? Pull up a dying or dead plant and split the stem open where the rot is. Do you see any hard black things looking like mouse poop?

I'll give the sm pot question a try: Generally, a smaller pot allows the roots to more uniformly fill the pot and thus suck the water out of all parts of the pot at about the same rate. So you won't have parts of the soil that are dry and other parts that are still wet...just ripe for mold/rot. A poster on here named Russ has mentioned this before, and he has maybe dozens(?) of Aroids. Here on the central east coast we've had an all time record rainfall total for the year. That has added to indoor humidity as well. As for the rot this year as opposed to other yrs: Depending on where you live, higher humidity than ever before could have helped the rot to prosper. I had an Elephant Ear get 2 deep rot areas on it's trunk/corm when storing it indoors for the winter. I scraped the rot out with a metal teaspoon and its handle tip. I felt terrible doing it because I didn't know what the outcome would be but I didn't want to do nothing. Only the softer areas were easy to scrape out so I only scraped those. Then I rinsed it with water, placed it next to a fan, and a couple days later when completely dry I sprayed copper fungicide on it. In my case I then stored it for a few months in a sm bag of peat moss - but in your case it would be re-potted. That was 12 mos ago, It did great over the summer when planted and produced a couple pups.

Shavedmonkey, I hink in nature the water runs away from the center of these because they are often seen growing downwards right? Because if they grow on trees and such the way the do in pots, the water after it rains would sit in the crown, am I right?

Since these types of plants are often propagated with multiple cuttings, it's possible that one strand just was never seated well in the soil or never fully developed good roots. So it never got enough water and the roots on that strand dried up. If the rest of the plant is healthy, I wouldn't worry too much about it. You can inspect the other strands at the base of the soil. Also, you may still be able to root that piece that came out. Remove the lower set of leaves and stick the strand in a small glass of water or dampened perlite. They develop roots fairly easily. If the leaves on it are still strong, you could propagate using the "butterfly method". This is what I did with the strands someone gave me recently. You can google it up. But basically, you cut the strand in pieces between each set of two leaves. Then lay them on top of some dampened soil or perlite and sort of push them down a bit to make contact. Wait. They will eventually start to grow. This was started about two months ago from a single strand that I cut up like that.