There were not a lot of responses to my HU post.
It seems that many people experience migraine aura without the headache, including several people that used to have the headaches but now only experience the aura.
I did do a bit of digging; I didn’t find a lot of peer-reviewed science, but there was a reasonable amount of anecdote and experience.
Most medical sites give the cause as abnormal brain activity affecting nerve signals, but this is obviously wrong; the abnormal brain activity would seem also to be a symptom, which itself must have an underlying cause.
Migraine auras do have an association with catheter ablations; the trans-septal puncture is thought to be the cause. A majority of people experience an aura within a day or so of the procedure and rarely experience too many. Even in the worst affected patients, the auras tend to stop after a few weeks as the puncture heals.
Triggers are routinely discussed online. Typical examples are stress, depression, anxiety, excitement, shock, tiredness / insufficient sleep, shoulder or neck tension, poor posture, physical overexertion, low blood sugar and jet lag. I think there is quite a lot of overlap with AF in there, but this does not suggest that migraines are a precursor of AF.