Thanks Jeff.
Somehow my Primary database didn't get back up (Full backup - nightly job) and that also happened previously.
I didn't see any error or message into log.
Last time when i deleted AG group then started to take the FULL backup.
TLog backup running fine that we are using via Sql Agent job.
Full nightly backup we are using 3rd party tool.
Any idea?
Thanks for your time and great help!