You may want to try finding out whether it’s CSIS or CBSA that’s holding up your file. From my research, CSIS can sit on files for a long time if they suspect anything out of the ordinary (not just obvious terror threats). In some instances, your name comes up on a “watch list” or there’s a poison pen letter. Something or the other to warrant further investigations. Studying Federal mandamus legal cases, it seems they're notoriously slow at this task and the more serious the issue (in their eyes), the longer they make you wait- sometimes to get info from foreign governments, but sometimes without explanation. In some instances, files mysteriously get "lost in transit" for a year or two then reappear. In some cases they look at a file once or twice a year and kick it down the road.
CSIS is a highly secretive and unaccountable organization and apart from formal complaints to the security intelligence review committee (which tend to be dismissed - reading the annual reports), there’s not much one can do but wait it out or are lucky to become eligible for urgent processing.
That said, it could have something to do with the backlog. June/July applicants have been seeing background cleared recently so we may be a few months away from approval.