Hey KK as per my experience it shouldn't take 18 months until there isn't any RED FLAG i.e. age difference, second marriage of PA or SPONSOR, different religion & background etc. But even in those cases it doesn't take that long cuz by law the maximum time frame for spousal cases is 1 year. All people who were in our group's ( Jan- June 2018 ) it took only 6 - 8 months max for whole procedure.
The sponsor in your case should contact to local MP asap even though it's pandemic all over the world & it's not easy to meet them in person but try to contact him / her by phone or email with whole case summary.
You can call CIC agents too or NDVO by phone or email as a reminder even though they don't reply to everyone but keep trying.
Main thing is after medical they gonna work on your background. It take maximum 3- 4 months moreover if they have backlogs then i seen they done it within week or days but seems like in your case they didn't that yet. On your gckey if it's show background check in PROGRESS that means they didn't start yet and if it's in PROCESS then it has been started.
So check your Gckey & confirm it and try to contact LOCAL MP IN CANADA, NDVO, CIC AGENT. Good luck to you bruv & hope you'll get it done asap.