How probable is it to vote before the reward cutoff time by chance? I assume greater for whales as they engage more, but with all my votes until now I never got the error message "Cannot increase payout within last twelve hours before payout." Does it still exist?

May I ask you also what you consider just before the reward cutoff time? It seems like anything 12 hours before or later.

And I can assure you @sweetsssj upvoting @missdeli is 100% deserved, which tells me that in this report you will find quite the one or other false positive.