Update: Yesterday the Air Force announced that it recovered the data (link).
According to this report:
The U.S. Air Force has lost records concerning 100,000 investigations into everything from workplace disputes to fraud.
A database that hosts files from the Air Force’s inspector general and legislative liaison divisions became corrupted last month, destroying data created between 2004 and now, service officials said. Neither the Air Force nor Lockheed Martin, the defense firm that runs the database, could say why it became corrupted or whether they’ll be able to recover the information.
The same report notes, however, that the investigations involving sex issues are safe:
Air Force officials originally said information on sexual assaults might had been lost in the crash. After the article was published, they said that while sexual assault and harassment claims might have been part of the files lost, those types of investigations are backed up elsewhere. The inspector general does not investigate cases solely involving sexual assault. However, sexual assault or harassment might be tangentially part of an inspector general investigation, a service spokeswoman said.