issued a highly critical analysis
Followed up with a pointed memo probably.
If the IG is issuing reports, they got the go ahead from the FBI because the release, will not affect their results. So, IMO, they know they are not going to criminally charge her. In my experience, the IGs do not issue admin reports when there is a criminal case pending FWIW.
I think the FBI has long since branched out into areas (Clinton Foundation, money laundering, pay to play, etc.) other than her home-brew server, although emails recovered from the server have given them the fodder to branch out.
The recent announcement of the Punk being investigation is probably related.