Of course, that claim is disputed, probably because it's a lie: https://pjmedia.com/news-and-politics/matt-margolis/2021/06/14/report-claiming-hundreds-of-thousands-ballots-missing-in-arizona-disputed-n1454565
Of course, some of the loudest preachers of the "election was stolen" lie, when confronted in court, back down and admit that "no reasonable person" could believe such hogwash. See, e.g., Sidney Powell: https://chicago.suntimes.com/columnists/2021/3/25/22350378/sidney-powell-admits-lie-mona-charen
For a good insight into how decent, patriotic Americans can be persuaded by the Comrade Commissars of the world to believe things that are utterly batshit crazy, read this: https://www.latimes.com/opinion/story/2020-12-06/donald-trump-election-fraud-lies-psychology