Two, Richard White. “Overturned” in four hours. Nick Nicholas’ answer to Why was Richard White banned from Quora? Again, no explanation given.
What there is on Quora about account banning seems to reflect the Elder Days, when there was community involvement in moderation. It is hard to believe, given the slew of bans in mid-2016, that the same level of deliberation and warnings that Konstantinos Konstantinides’ answer recalls is happening now.
EDIT: Whatever the frequency of ban reversals was before, they’re not uncommon nowadays: see Necrologue.