The surprises keep coming in former National Security Adviser Michael Flynn's legal battle to overturn his conviction in the Russia probe.

Just days after the FBI belatedly produced possible evidence of innocence to Flynn's new legal team led by Attorney Sidney Powell, his old law firm on Tuesday informed the judge it had located 6,800 documents that it failed to turn over as required by a court order in 2019.

Covington & Burling LLP told the court its search team failed to search all of the law firm's records and missed the documents, mostly emails. The documents were produced to Powell on Tuesday.

"Covington determined that an unintentional miscommunication involving the firm’s information technology personnel had led them, in some instances, to run search terms on

subsets of emails ... rather than on the broader sets of emails that should have been searched," Flynn's former attorney Robert Kelner told the court in a motion.

"We now have performed another search, using search terms and manual reviews, on a broader universe of material to correct the earlier error and to transfer additional documents that are part of the client file," Kelner wrote, saying his firm was willing to assist Powell on any other matters and to address any questions the judge may have about the oversight.

You can read the motion here.

Flynn was forced to step down as President Trump's former national security adviser just weeks into his new job after a transcript of his calls with the Russian ambassador was leaked to the media, raising questions about whether he was part of an effort to collude with Moscow.

Flynn eventually pled guilty to a charge of lying to prosecutors and became a cooperating witnesses for Special Counsel Robert Mueller, who ultimately concluded there was no evidence Flynn or any other Trump official conspired with Russia to hijack the 2016 election. His plea deal was reached while he was will represented by Kelner.

Powell took over as Flynn's new lawyer last summer, and the judge in the case order Covington to turn over all defense documents to her.

Powell has tried to reverse Flynn's guilty plea, dramatically alleging that FBI agents sought to "frame" her client on an unwarranted charge of lying and that Mueller's team and Covington improperly hid from the court that Flynn's plea deal was connected to a side deal not to prosecute his son.

The court is expected to make public soon the new, but still sealed, FBI documents that were belatedly turned over to Powell, which she argued in a Friday court motion provided evidence that agents engaged in misconduct during the Russia probe.