High unmanaged disk usage on /ngfw cisco FMC/FTD error

After upgrade to 6.7 I got this error in the FMC health section:

High unmanaged disk usage on /ngfw cisco 

Going into the CLI is appeared there was space.
It looks like a bug CSCvc03899. 
Some old install files left behind. 

You need to remove them but you won't be able to roll back to that version. My system was stable and I had taken a backup of the FMC and managed device on 6.7 and no intention to roll back to any previous version anyway.

From CLISH (>) run cleanup-revert
> upgrade cleanup-revert
It is not possible to revert back to the previous version once the revert version is deleted.
Are you sure you want to proceed (yes/no)? yes

Go into expert mode and then (sudo su -)

Find old version files
FTD#cd /ngfw/Volume
# du -hs * | sort -rh
7.3G 6.4.0 ---> old version
6.9G root1
4.1G lib
116K home
0 root

Delete old version files Delete 6.4.0 file as below:

/ngfw/Volume# rm -rf 6.4.0
# du -hs * | sort -rh
6.9G root1
4.1G lib
116K home
0 root

FQDN on palo alto firewall

Show all the fqdn's that are resolved

show dns-proxy fqdn all

DNS servers are configured under