Weird Root

This already happened to three of my phals' roots. I've noticed all three are aerial roots, new nice healthy long aerial roots. But they got this type of "rot" that attacked the middle of the roots. The attacked portions are brownish. This is strange because the plants are all really healthy, and suddenly came the mysterious root problem. It's been a while since I'd noticed these, and the unaffected portions of the roots are still alive.

Here's a pic. Any idea what's causing this? Anything I can do?

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I got that kind of problem too with my Phals whenever I let thier roots stray out of the pot that far. I always thought that it dried up because its not getting enough moisture .

Might be from some type of damage to the root in that area , The end piece will probably dry up , if goes any farther toward the plant part I would remove it to the healthy root growth , the root might side branch . Gin