When Nader flew into Dulles Airport outside Washington in January 2018, he was questioned by agents working for Mueller. A search of three iPhones seized from him that day via a search warrant allegedly turned up child pornography.
Prosecutors filed a criminal complaint against Nader over the images in April 2018 but kept the charges under seal and never told his attorneys about them even as he continued to cooperate with Mueller's probe, lawyers said.
https://www.politico.com/blogs/under-the-radar/2019/07/19/george-nader-mueller-probe-child-pornography-1422642
I don;t believe any of the allegations involve activity post-disband of the Weissman/Mueller with hunt.