A poll observer identified the error that resulted in Milwaukee officials' decision to rerun approximately 31,000 absentee ballots earlier today.

Milwaukee's top election official said that the city's election results will likely be reported in the "early morning hours" after an error at a central processing location forced a retabulation of those ballots.

Milwaukee Election Commission Director Paulina Gutierrez said the error was identified by a poll observer -- a member of the public who watches election officials for the sake of transparency.

The Trump campaign criticized Milwaukee election officials for the error.

"This is an unacceptable example of incompetent election administration in a key swing state: voters deserve better and we are unambiguously calling on Milwaukee's officials to do their jobs and count ballots quickly and effectively," RNC Chairman Michael Whatley and Co-Chair Lara Trump said in a statement.

"It's a human error," Gutierrez said. "That is the point of central county elections, is that it's transparent, and the observers brought it to our attention."

A top Cybersecurity and Infrastructure Security official said there is "no evidence" that there is cheating in Philadelphia and Detroit as former President Donald Trump has claimed.

"We have been in very close contact with state and local election officials across the country, and we see no data or reporting to support these claims," Cait Conley, the senior adviser to the CISA Director and head of elections said on a call with reporters.

Nationally, Conley said officials "are not currently tracking any significant incidents with national level impacts to election infrastructure security."

Additionally, she said officials expect to see Russian disinformation actors piggyback off the hoax bomb threats that were sent to Arizona, Georgia, Michigan and Wisconsin by the Russians.

"We should not be surprised if we do," she said in response to a question about Russian actors using the hoax bomb threats. "Our adversaries are specifically intent on leveraging opportunities to spin narratives to undermine confidence."

-ABC News' Luke Barr

There are "residual issues" including long lines at the polls in Apache County, Arizona, after the machines that print ballots "did not work as planned" Tuesday morning, state officials said.

The countywide issue was fixed earlier in the day and most sites in the county are "up and running well but as we understand at this moment, there are still some residual issues out in Apache County," Arizona Secretary of State Adrian Fontes said. "We're doing our best to work with county election officials there to see if we can resolve any of the remaining problems."

Rita Vaughan, the elections director for Apache County, told ABC News that "all polling places have remained open and voting has continued all day for registered voters who want to cast their ballots."

-ABC News' Laura Romero

Milwaukee will have to retabulate approximately 31,000 absentee ballots after a human error at the city's central ballot processing location, likely delaying the city's final results by hours.

A door to several tabulators was not properly sealed, according to Jeff Fleming of the Milwaukee mayor's office.

"The people operating the machines along both walls -- the 13 machines -- are being reset to zero," Fleming said. "They will rerun all the ballots that they previously ran after it has been reset."

Milwaukee received a total of 106,000 absentee ballots, which are processed at the city's Baird Convention Center. The city cannot report the results of the absentee ballots until every ballot is counted, per Wisconsin law.

"We're guessing, you know, one hour, two hours, three hours, four. We just don't know at this stage," Fleming said about the delay.

Fleming said the issue was "human error" that he blamed on "senior election staff."

"We want to make sure everybody understands that our goal here in this room is to be absolutely accurate beyond any question, and to do that, we're going to rerun the balance," Fleming said.

The Milwaukee Election Commission said that the doors to the tabulators were not “fully in place,” forcing a restart of the process.

“The City of Milwaukee has no doubt regarding the integrity of the election," the commission said in a statement. "However, in order to eliminate any doubt to be fully transparent, the MEC has decided to start the tabulation process over for all ballots at Central Count."

-ABC News' Peter Charalambous