This new paper from Herron, Smith, et. al., out incredibly fast, suggests that there were 4,000 people in Gwinnett County who accidentally voted twice in the Loeffler-Collins-Warnock race, due to confusion of the double-column ballot used there. Pictures of the ballot in Gwinnett County compared to the one in Bibb County, from their paper is below. This has no effect on the presidential election and did not affect the outcome in the Senate race, but a possible example about how badly designed ballots can confuse voters: