Resolved. It could have been two things.
1) It might require the python-inotify package?
$ sudo yum -y install python-inotify
The original import directory was a NFS share, bind mount with read/write access only to that directory.
I noticed calibre hadn an error trying to access the trash. SError: [Errno 13] Permission denied: '/nfs/books/.Trash-1000' - which is right. It's read only except for the imports dir.
I decided to skip using nfs/bind mount since the import dir only houses books temporarily. Used a local import dir and haven't had any issue now.