For most cases, its coinciding with criminality check renewal as some members mentioned. In few cases, there will be status change in the next few days.
My wife received gcms this week and it was coinciding with background check renewal after 1 year of criminality passed last year. So i assume that it was the case for me and my wife.
My ghost update was in oct hence no updates immediately after ghost update since there was no real progress to the application itself except background recheck.
My DM and oath date notification came only this month, after i emailed my processing office to consider finalizing my file since its been 2 years.