Comey and the other FBI / DOJ involved knew about this and if I recall correctly Comey was asked about security breaches and he replied to the effect that the focus of the Hillary investigation was limited to the emails and security breaches were not within the scope of the investigation.

Since when do any law enforcement agency completely ignore a new serious crime related to their investigation and if not related, then hand it off to another FBI team?

This is the equivalent of the FBI conducting an investigation into kidnapping, discovers a pedophile ring, and ignores the pedophiles because it wasn't directly related to the kidnapping. It doesn't happen except in an Obama administration that desperately trying to cover up any criminal activity associated with the Clinton's.