The documentation might get you a bit confused, but after have a chat with Cisco TAC they shed some light…..Unfortunately this design is not supported, so if you are migrating from a Old Cisco ASA platform it’s time to redesign and avoid redundant interfaces. So i had to move those interfaces to port-channel, so the trade-off was the failover if the principal switch died.
And here is the bug reported
Redundant interfaces are not supported on all FXOS platforms
CSCvg30354
Symptom:
“Firepower Management Center Configuration Guide, Version 6.1”
Chapter: Interfaces for Firepower Threat DefenseInformation related to Redundant interfaces should be changed
FROM
Redundant interfaces are not supported on the Firepower 9300
TO
Redundant interfaces are not supported on the Firepower 9300, 4100, 2100Conditions:
Currently Redundant interfaces are not supported on all FXOS PlatformsWorkaround:
“Firepower Management Center Configuration Guide, Version 6.1”
Chapter: Interfaces for Firepower Threat DefenseInformation related to Redundant interfaces should be changed
FROM
Redundant interfaces are not supported on the Firepower 9300
TO
Redundant interfaces are not supported on the Firepower 9300, 4100, 2100Conditions:
Currently Redundant interfaces are not supported on all FXOS PlatformsWorkaround: