that's the problem. They are not in Inbox too.
So to test, I deleted all the library and created a new one again with only few albums around 10 which includes the missing album.
I selected to import all the songs to Inbox.
The file scanning lists correct count in the scanning(i.e., 50 files scanned) but after scanning, the album is missing in the Inbox too.
Looks like some kind of issue in Musicbee