Your timeline looks remarkably similar to mine, just shifting a few months since the start. My BG was idle for about a year until I did a ATIP on CSIS, then almost right after I submitted the ATIP request, CSIS completed their task and BG was completed. It may look like a coincidence, but doesn't hurt to try that if you haven't already.
Another thing happened recently was I received IRCC GCMS notes I requested about a month ago, and oddly my secondary office changed from 8090 Sydney to 3193 Domestic RO. I don't know if you have requested for GCMS lately or not, but I am curious to see if your secondary office has changed as well. On the 8090 thread another person indicated their secondary office changed to 3193 as well. I hope this isn't IRCC's way of playing games with names and just changing all 8090 into 3193 to clean slate.