It's your basic localised supercharged low pressure bubbles, due to the magnetic fluctuations causing high energy particles to stream into minor holes in the lower magnetosphere.

The supercharged particles are heated from the energy and a lot become ionised and spread out to cause a relatively small sphere of low pressure and little oxygen, most the oxygen will be ionised and useless anyway.

Can only be sustained via a constant input of energy and so most are short-lived.

Nothing sinister, the low pressure knocks them out cold from lack of oxygen, some wake up as they leave the low pressure bubble, but they have already suffered severe internal damage from the lack of oxygen and the sudden low pressure that they cannot continue to fly.