© NBCButtigieg boldly claimed Iowa victory before results had been issued.
The error, which caused accurately collected data to only be partially reported, pushed the party to resort to manual backups.
"As part of our investigation, we determined with certainty that the underlying data collected via the app was sound," Iowa Democratic Party chairman Troy Price said in a statement. "While the app was recording data accurately, it was reporting out only partial data. We have determined that this was due to a coding issue in the reporting system. This issue was identified and fixed."
Price also said that the party has been able to verify the vote counts through "required paper documentation," but did not promise that results would be reported on Tuesday.
"Precinct level results are still being reported to the IDP," he said. "While our plan is to release results as soon as possible today, our ultimate goal is to ensure that the integrity and accuracy of the process continues to be upheld."
Price said there was no indication of any outside effort to affect the app or the reporting of results.
"We have every indication that our systems were secure and there was not a cyber security intrusion," Price said. "In preparation for the caucuses, our systems were tested by independent cybersecurity consultants."
But the app appeared to have problems even before the "coding issue."
Early Monday, Democratic county chairmen in Iowa said that some of their precinct leaders had trouble downloading and installing the app, and others received error messages. Two of those chairs said they were going to use manual methods and call the results in on a hotline.
Caucus managers reported extended wait times on the hotline, leading to frustration and confusion.
"I waited on hold for 20 minutes and gave up," said Jennifer Herrington, a caucus chair in Page County, Iowa. "They were asking for first alignment results and final results, plus delegates. In 2016, it was an automated call reporting system that just asked for delegates. Seems they tried to fix what wasn't broken."
Shawn Sebastian, the caucus secretary for a precinct in Story County, said he was on hold for 90 minutes waiting to report his results.
Some precinct captains and caucus organizers also expressed doubt about the app in the days leading up to the caucuses. An email chain provided to NBC News showed that precinct captains and caucus organizers in the Iowa City area knew of problems with the reporting app as early as Monday morning. The email was shared on the condition that identities would be redacted.
"Nobody having trouble with the app should feel dumb!" one of the organizers wrote on Monday morning. "I am hearing way more problems than in 2016... Worst case, call it in, which I expect 90% of the state will be doing anyway."
"I gave up on the app," another precinct chair replied.
The app was the subject of scrutiny in the weeks before the caucus due in part to the lack of information around it. Before the caucus, the Iowa Democratic Party declined for security reasons to say which company developed the app. It so far hasn't responded to new requests to confirm the app's maker.
The app is also set to be used in the upcoming Nevada caucus on Feb. 22. The same company developed both the Iowa and Nevada Democratic party caucus apps.
Two Democratic strategists familiar with the matter told NBC News that the app developer was Shadow, Inc., a technology company focused on helping progressive candidates. A review of public records by NBC News show payments this winter of over $50,000 by both the Iowa and Nevada Democratic parties to the developer.
The company was funded by Acronym, a Democratic political non-profit, according to Acronym founder Tara McGowan.
McGowan said on Twitter that Acronym is a nonprofit and an investor in several companies including Shadow.
Some election security experts questioned why an app was necessary to conduct the caucus.
"In years gone by the results were phoned in," said Greg Miller, cofounder of Open Source Election Technology Institute (OSET), a nonprofit that conducts election technology research. "And we're lost as to why that had to change, making this is a solution in search of a problem."
Since 2016, NBC News has collaborated with the OSET Institute to monitor U.S. election-technology and voting issues.
Ben Popken is a senior business reporter for NBC News.
Oh who cares. They're just wasting their time anyway, and they know it.
They would have better luck just playing Minecraft on their Apple crap.