It affects some people much more than others, it's not a uniform random occurrence, so a person with one blackout is more likely than most to have more than one

It affects some people much more than others, it's not a uniform random occurrence, so a person with one blackout is more likely than most to have more than one. Some people are very anxious during interviews, and their frontal lobe basically shuts down, others love interviews. So it's very likely that many of the people you've interviewed who you thought "couldn't code" actually just couldn't code while you were watching them.