Anecdotal reports in this forum do NOT reveal much about what happens in "Secondary Review" for a PR card application. Indeed, most reveal near nothing except the process often takes more than six months and up to a year, with some going faster and some going beyond a year. Most reports indicate that after getting notice of the referral to Secondary Review there are NO further communications or requests from IRCC UNTIL the PR gets the PR card in the mail or a notice to pick up the card in person in a local office.
Most is NOT all. There are variations. But personal reports of Secondary Review in this forum are mostly about a long delay in completing the process of issuing a new PR card. Then, suddenly, with little or no notice, it is done.
That said, without attempting a statistical analysis, the number of forum participants who have reported being subject to "Secondary Review" when in fact it is apparent they were subject to some other type of additional review, not what IRCC refers to as "Secondary Review," may actually exceed the number of reports, here in the forum, of what really are referrals to Secondary Review.
There is a topic specifically devoted to the subject of Secondary Review (and it is also discussed in some depth in other topics as well). That topic is titled Email from CIC that PR card renewal needs secondary review"
see
https://www.canadavisa.com/canada-immigration-discussion-board/threads/email-from-cic-that-pr-card-renewal-needs-secondary-review.251571/
The problem, again, is that discussion mixes multiple types of review often without distinction. Many forum participants describing this or that about their experience say they were referred to Secondary Review when it is clear it was some other process, some other type of review, they actually experienced.
Another problem is that IRCC is NOT transparent. While those who diligently pursue keeping track of changes in operational manuals and operational bulletins and the PDIs can keep abreast of the more salient changes in policies and practices, actual methods and means are strictly confidential and not disclosed to the public. IRCC currently employs a very broad concept of what constitutes methods and means. So a great deal of the process is confidential. Behind the curtain which itself is behind closed doors.
Add to that the boilerplate structure of IRCC communications which largely appear to be electronically composed oriented to data fields, and NOT composed by a human intellect oriented to personal communication. For many IRCC clients all that is apparent is the formal request for this or that information or document, with little or NO explanation of why, little or no explanation as to what the process is.
There can be clues. For a client with a PR card application in process, for example, who receives a request for RQ related information (residency/presence questionnaire type requests), if the request comes from CPC-Sydney and the address for submitting the response is Sydney, that appears to be a different process than if the request directs the PR to submit the response to a local office. The former appears to be some type of Program Integrity (PI) or Quality Assurance (QA) screening and so far this does NOT appear to delay the process much. The latter, where the response is sent to the local office, that appears to usually be a more or less full-blown formal Residency Determination. Neither are "Secondary Review."
BUT so far as has been reported, the communication sent to the PR does NOT distinguish one from the other, except what we can interpret based on the address for submitting the response.
Another fulcrum of confusion in the forum derives from the correlation of cases in which the PR was
cutting-it-close relative to PR Residency Obligation compliance (
cutting-it-close is having less than 900 days presence, albeit the fewer days present the more the PR is
cutting-it-close) AND referrals to Secondary Review. It is readily apparent that the more the PR is
cutting-it-close the higher the RISK (probability) the PRC application will be referred to Secondary Review . . . BUT IT IS CLEAR THE FOCUS OF SECONDARY REVIEW IS NOT MERELY ABOUT RO COMPLIANCE, at least not as of the date the PRC application was made. So far as forum reporting goes, it appears RARE for a PR referred to "Secondary Review" to get RO compliance related requests for information or documents.
Indeed, it appears that Secondary Review is very often involved when IRCC perceives the PR to be living abroad . . . as if IRCC is holding up processing the PR card waiting to see if the PR will remain outside Canada and fail to be in compliance with the RO as of a future date, either upon arrival at a PoE or upon applying for a PR Travel Document to facilitate a return flight to Canada.
There are, obviously, other scenarios underlying Secondary Review cases. Some appear to involve investigating whether there have been misrepresentations made along the way, either in the original PR application process, or during a PoE examination, or in the application for a new PR card. But again all this takes place behind a curtain which is behind closed doors, so we know very little about what is actually happening.
BOTTOM-LINE: The majority of PRs who have not been gaming the system have very little to worry about Secondary Review . . . other than the fact of the potentially lengthy delay in getting a new PRC. If there is something to worry about, odds are very high the PR is already aware of that AND why. (Protests to the contrary tend to lack credibility.)