Not really complicated. There is very little "processing" involved when a PR Card application is routine. Most PRC applications are decided when they are opened or very soon after that, and the only other steps or actions taken are those to physically issue a new card and deliver it.
For the routine application it is basically about establishing the identity of the applicant (the PR) and establishing their PR status (this takes just seconds in GCMS, but processing agents are probably allotted a number of minutes to do this), and reviewing the information in the application to determine if there are any reasons to question the PR's presence in Canada. If there are no questions, no concerns, done. Application approved and referred to whoever does the issuing of a PR card and then on to mailing.
If upon opening the application a processing agent has questions, concerns, or cause to initiate investigatory processing, typically in regards to the PR's presence in Canada and compliance with the Residency Obligation, the application is subject to non-routine processing. That means going into a queue for another processing agent to assess and deal with whatever reason tipped the application out of the routine processing work flow. The wait time is queue time. That can go long.
See or start another topic for discussion about particular non-routine procedures for PRC applications; they can range widely, ranging from those reviewed and approved without problem (other than the delay in time, mostly spent in queue waiting for an agent to take this step), to referral to a local office for investigatory processing, or referral to Secondary Review, with potential side trips along the way. Secondary Review, in particular, tends to result in rather lengthy timelines. That said, one of the side trips for approved applications can be in-person pick-up, which in normal times only delays getting the card by a matter of weeks or a couple months or so, but during Covid-times has resulted in a more or less indefinite delay, and is a situation which appears to still be in limbo.
More than a few PRs seem to think that because they know they have complied with the PR Residency Obligation, IRCC should not have any questions or concerns. Not how it works. Especially for those cutting-it-close, those with more or less obvious on-going residential ties or employment or businesses abroad, those with certain patterns of travel indicating a possibility they have not settled permanently in Canada, among other factors or circumstances which might trigger elevated scrutiny . . . meaning non-routine processing . . . meaning a significantly longer timeline.
For comparison purposes: Not sure, but I also suspect that minors, at least those who appear to be IN Canada, benefit from some positive presumptions that may lean heavily in favour of approving the issuance of a new PRC without delay.
