I hate being a conspiracy theorist here but I'll stick to this opinion unless proven otherwise (which means "unless they issue me a PPR", but perhaps even after that).
I am almost certain it is a subtle way to filter out some applicants who look less desirable than others. Since technically Express Entry has no country or skillset limits, they can't say "we want only software engineers without kids from countries A & B" or "we want healthcare professionals currently residing in the UK or USA", IRCC just processes the more desirable ones and puts applications of a lesser priority on a hold of sorts. Maybe not an indefinite hold. If you look at the trackers, it happened pre-covid as well.
Conspiracy theory session over, thank you.
