After recently deploying a new Firepower 3105 HA pair for a client, they decided to move the firewalls to a different rack. Upon powering up the devices, the secondary firewall wasn’t coming online and syncing with the primary.
We plugged a console cable into the device and were greeted with a ROMMON prompt:
rommon 1>
This lines up pretty well with the following BugID:
https://quickview.cloudapps.cisco.com/quickview/bug/CSCvp57772
While the workaround mentions doing a complete reimage of the device, there is a much simpler fix.