A spokesman for the FBI and a spokeswoman for the Justice Department declined to comment.
Congressional Republicans have been focusing on Strzok and Page in recent weeks after learning the two had exchanged anti-Trump text messages on their work-issued cell phones.
Republicans have said the texts, which referred to Trump as an “idiot” and a “loathsome human,” raised concerns the FBI is biased against Trump and may have given Clinton favorable treatment after deciding not to recommend criminal charges in connection with the probe into her use of a private email system while she was secretary of state.
Strzok and Page were involved in that investigation and also were briefly assigned to work with Special Counsel Robert Mueller on the Russia investigation.
After Mueller learned about the texts, Strzok was re-assigned to a different post. Page’s 45-day detail on Mueller’s team ended in July.
In his letter, Johnson said he learned of the software problem from the FBI on Jan. 19, after it gave 384 texts to the committee, one of several in Congress that recently launched inquiries into how the FBI handled the Clinton investigation.
“The loss of records from this period is concerning because it is apparent from other records that Mr. Strzok and Ms. Page communicated frequently about the investigation,” Johnson wrote.
He cited examples, including an exchange between Strzok and Page that took place in May 2016, after it became apparent that Trump would likely be the Republican presidential candidate.
“Now the pressure really starts to finish [midyear exam],” Strzok wrote, in what Johnson’s letter says is a reference to the Clinton investigation.
“It sure does,” Page responded.
In his letter, Johnson asked the FBI to follow up with more details about the scope of the lost records, and to tell the committee whether it has conducted searches of their non-government issued devices.
More about: #Hillary-Clinton