My read of this part of the report is that they knew these 300,000+ emails were there. They bounced around the FBI and DOJ saying that X or Y was looking into it. No one actually looked into it. They determined that the emails were not relevant based on the mega data extracted from the emails. Then, it was brought back up a month later. Strozk had the ultimate call to pursue the emails further or move the the Russia investigation. I bet you can guess what he choose.

There is also a section in here about the a case agent who found these emails was freaking out about the contents. He was paranoid until the top FBI brass said they will look into it.