It's not a myth, and has been seen reliable witnesses. Its mostly likely cause is that occasionally, ionization-induced plasma outputs RF that by accidentally matching of volumetric parameters (size) creates a self-sustaining RF discharge, where the RF continues to maintain the plasma and vice versa. A circular mechanism. Obvious it cannot last forever, but the plasma has enough stored energy to keep the cycle up for awhile. As a charged ball it may be affected by earth magnetic fields and then it moves. At some point the stored energy, through energy losses, drops below the minimum needed, and the ball self-destructs by expending its total energy rapidly. Tesla accidentally produced such balls, but repeatably, identifying that it is some arcane physics phenomenon and not myth. My personal guess is that it requires not just gasses but some seeding chemical, maybe dust of particular kind.

Not a myth. Search Arxiv.org for free to access scientific papers on the fields of physics. Do note that not all of them are peer-reviewed or experimentally verified:

https://arxiv.org/search/?query=ball+lightning&searchtype=all&source=header

Ball lightning went into the house my parents built in Bar Harbor 40 years ago. They wouldn't have any reason to lie about it. Said it broke their tv and was super strange.

If the ball lightning was observed following airliners then maybe they were seeing what we now attribute to UFOs?

It's been a very long tie since it was considered to be a myth