I think that it's a harmless fungus ... which thrives on dead vegetation, left by the grower cutting off leaves, rather than snapping them off at the trunk.

You can pull these dead stem stumps off ... if you wish.

I think they all look like they're just a bit of TLC away from being really nice plants. Were they mine, I would scrape a good bit of that tree bark off the stem, repot a little lower and let them grow. I agree w aegis as far as how it looks. Doesn't look fatal.

Siri might weigh in here shortly. She definitely has the medical books locked up w regard to these AV's. She will be able to say for sure.

I agree with the other two! The first one just didn't get those stems plucked off. Some shaping, some replanting will have it very happy.

The second one is indeed gnarly; it's really lopsided, so I think restarting the crown might be best for it. I'm sure you've done all that research already, but here's a way to go about it:

1. Sterilize a blade with isopropyl alcohol; I use boxcutter blades--set aside.
2. Take the plant out of its old pot, dust it off, and peel away outer leaves until you have a small, symmetrical crown (2 or 3 rows of leaves will do).
3. Chop off the roots--cut point is wherever the stem looks healthiest and straightest. I would scrape it a little too.
4. Root the plant in whatever medium you like to use, and feel free to bag it in a ziploc until it roots (I live in a valley, so I open the bag for air every 2-3 days). Make sure it's a big bag--plastic touching the leaves can cause issues.

I believe in them and you! From looking at your other photos, I can tell you know what your green friends need. :o)

Thanks for your explanations and Marina for your directions. So helpful and reassuring!