After re-image FPR2110 from FTD to ASA9.8.2, the chassis (FXOS) mgmt interface UI become unaccesible giving the following error “Forbidden- you don’t have permission to access / on this server”.
In a nutshell, i could access FXOS via SSH and ASA (SSH & HTTPS) but the FXOS Chassis Management was broken. After spend some time, the only way to get this sorted was upgrade for the version 9.9.x
After upgrade, everything was working again.