Hello all, I'm an air traffic controller operating airspace in the eastern chunk of the North Atlantic. There have been a big increase of these sorts of reports from aircraft recently. We often get asked "is there any military activity?", but nothing displayed on radar.
Occam's razor to me just says satellites flaring, as often the reports are similiar to the comments above, where the sightings are higher and far away, brightly lit before suddenly dimming, which is consistent with solar flaring. If you sit outside and watch for a while you will see the ISS flaring and dimming as it passes overhead. I know you are all well aware of that, and what satellites look like though. You're the ones up there seeing them every night of your working lives.
However yes the swirling/ziz-zagging effect that flight crews are seeing is perplexing and hard to explain. Perhaps what we are seeing is just multiple satellites/starlinks suddenly flaring/dimming quickly, and giving the effect of individual movement, when in reality it is a group transiting in and out of view, displaying an illusion of rapid direction/velocity change etc. Just a hypothisis. It is a strange one though. Maybe we are actually being infested with other flying objects and our commercial airspace isn't as pristine as we like to think it is.
We did have an interesing report from a crew at FL410 very recently saying they saw a group of bright lights "below and dogfighting" at 0500utc, we attirubuted that to some training sortie getting airbourne off a aircraft carrier without telling anyone, or maybe what looked below was just far away and actually well above.
Who knows. It's always curious to get reports though, makes night duties a bit more interesting.
Reports always seem to increase from November onwards every year though, which makes me think it's related to a lower winter sun relative to the viewing position causing increased visual flaring events.
Kudos to Flarkey above for their efforts and for applying science and reason.