Unable to open database /data/freenas-v1.db

I noticed recently I cannot get any email with smart report etc. It says
“Error: unable to open database ‘/data/freenas-v1.db’: unable to open database file”
when I try to run script with shell command.

What is the reason of this error? I can backup config file manually. Is there any way to copy backup file to data folder (to restore freenas-v1.db file)?

Also, when I login with root account I cannot reach /mnt/ folder in shell. I cannot see mnt folder when I list the folders. But I can reach this folder (all folders) if I login with other admin account that I created.
Why I cannot reach mnt folder with root account?

Version: FreeNAS-11.3-U5

Thank you for your help.