In an Oakland polling place people were told they could take their ballot home after they voted, that it was just a receipt. Turns out that the workers were wrong and over 150 people had their votes invalidated. Biden won by ~80% in that county so most of the votes have been for him.
https://www.latimes.com/california/story/2020-11-13/oakland-voters-wrongly-told-ballot-receipt-2020-election