I think you'll find that the newest applications for study permit that have not yet been examined are undergoing the 2 stage process, whereas older applications have already been examined and fully approved but IRCC are holding back on telling applicants, therefore those older applications already fully approved, so some IRCC offices are starting with the newest applications. Then some IRCC offices are starting with the oldest applications! It seems to be one end or the other, oldest should be from February 2020. Ordering notes on older applications will confirm this that in fact the entire study permit is already approved. Each IRCC office has slightly different levels of applications whether family reunification / visit / study permit / work permit eg Delhi possibly has the highest number of applications as Indians seek to emigrate via the student route and Indians make up around 30% of Canada's international study body, therefore some offices are taking longer to work backwards through applications than offices where study permits are very high compared to IRCC offices where study permit applications are a lower proportion of the workload.