It would seem that basically everyone at the FBI is leaking their sides of various internal disputes and turf wars, largely tied to various investigations of the Clintons or attempts to start investigations of the Clintons. That alone paints a picture of Director James Comey as having totally lost control of the organization.
The upshot, from Barrett's reporting, is that basically everyone at the Justice Department thought the investigators didn't really have anything. Seemingly, that opinion was shared among senior officials at the FBI. But the agents, who seem to have started the digging basically on their own, were sure they did. They were repeatedly told to move on, they didn't have anything. But they seemed to keep pursuing it regardless.
there's very little to shake Democrats of their longheld belief that the rank and file of the FBI has a strong Republican lean (like most law enforcement, to be fair) and that that not infrequently bleeds out in high profile public corruption probes - especially when it comes to the Clintons.
a pretty toxic situation with FBI agents pursuing probes prosecutors believe have little merit, leaking to congressional Republicans and finding various ways to force their probes into the public.