Mistakes in implementing the ban on new paid advertisements led to US Republicans and Democrats blaming Facebook of undermining their respective campaigns.
To be in position to be used in days ahead, ads in Facebook library have to have run at least once
Confusion over political ads at Facebook marred the onset of what was supposed to be a cooling period ahead of the US presidential election.
Mistakes implementing a ban on new paid advertisements at Facebook during the week leading up to November 3 had rival parties complaining the leading social network was undermining campaign efforts.
"We're investigating the issues of some ads being paused incorrectly, and some advertisers having trouble making changes to their campaigns," Facebook product manager Rob Leathern said in a tweeted message when the ban kicked in on Tuesday.
"We're working quickly on these fixes."
California-based Facebook has tightened its rules on political advertising ahead of the 2020 election. In particular, it has prohibited attempts to undermine the electoral process.
The social media network also banned new political advertising in the week before the November 3 election. That ban kicked in on October 27.
Political advertisements could sidestep the ban by getting in position at Facebook prior to the deadline, with those behind them deciding when to activate them.
President Donald Trump's campaign displayed in a paid posts library at Facebook included what appeared to be a victory advertisement.
The animated advertisement showed a cartoon sunrise along with a smiling Trump head atop a flitting bird and a soundtrack featuring an agonised cry of "No" after the claim Trump was still president.
Megan Clasen, a senior media advisor for Democratic presidential contender Joe Biden, tweeted a screen capture of a Trump ad with a picture of the president and a message that "Election Day Is Today."
Former vice president Joe Biden's campaign was told by Facebook they could not launch advertisements saying election day was "today" or even "tomorrow," Clasen said in the tweet.
To be in position to be used in the days ahead, advertisements in the Facebook library have to have run at least once, if even to a just a very limited audience.
"When Facebook's latest ad policies were announced, we warned that they contained major loopholes that would likely enable election misinformation," said Media Matters president Angelo Carusone.
"Now we are seeing those warnings come to life."
Democratic political strategist Eric Reif put out word on Twitter that he and other were working to have advertisements mistakenly removed by Facebook restored at the social network.
Facebook chief Mark Zuckerberg was grilled on Capitol Hill on Wednesday, with decisions regarding political content a hot button topic.
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