Not only the mistake of 9000 votes, but a shortage of Republican poll watchers.
thefederalist.com
Georgia Republican Poll Watcher Discovered Recount Error Off By More Than 9,000 Votes For Biden
“One batch was labeled 10,707 for Biden and 13 for Trump — an improbable margin even by DeKalb standards. The actual count for the batch was 1,081 for Biden and 13 for Trump,” Shafer said.
“We were limited to 1 monitor for every 10 counting tables and we were kept some distance from the tables,” he wrote. “There is no telling what we missed under these unreasonable restrictions. The miscounted batch had been signed off by two official counters.”
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Georgia Republican Poll Watcher Discovered Recount Error Off By More Than 9,000 Votes For Biden
A batch of ballots in DeKalb County was labeled as containing 10,707 votes for Biden, but in reality it contained 1,081 votes for Biden.

Georgia Republican Poll Watcher Discovered Recount Error Off By More Than 9,000 Votes For Biden
“One batch was labeled 10,707 for Biden and 13 for Trump — an improbable margin even by DeKalb standards. The actual count for the batch was 1,081 for Biden and 13 for Trump,” Shafer said.
“We were limited to 1 monitor for every 10 counting tables and we were kept some distance from the tables,” he wrote. “There is no telling what we missed under these unreasonable restrictions. The miscounted batch had been signed off by two official counters.”
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