Sshd_config cant save config

My Cloud OS 3 Personal & Network Attached Storage My Cloud EX2
1

Hello
I try de back up some ubuntu pc on my NAS EX2 ,i write
" AuthorizedKeysFile /home/root/.ssh/authorized_keys " to /etc/ssh/sshd_config
the problem is when i restart ssh service or restart my NAS ,the file sshd_config appear to be resetted and i lose my changement.
is there an explication to this plz