xotic said:
Any idea how long it takes if your case is sent to CSIS for clearance AFTER the test and interview. Checked GCM notes, nothing in there. Reason for CSIS clearance I believe could be that I belong to a country considered high security risk. Any one who went through this and got the citizenship? I know it would be different in every case, just want to know if I am in for a long haul.....how long a haul

and if it will come to end at all !!! Also has anyone's citizenship been declined/ rejected for security reasons.
Comments are solicited and will be appreciated.
I have no personal experience, and I am no expert, and a significant part of what I know in particular about the background checks, including the CSIS security check, is related to information obtained a few years ago (2012 and 2013 ATI responses).
I can, however, offer some observations:
Foremost, you are absolutely right on point in recognizing that what is involved and how long it takes for the CSIS security check, is indeed very different depending on the individual involved. There really are no general observations beyond this, beyond recognizing that how it goes will depend on the particulars of the individual case.
It warrants noting that for the vast majority of applicants the delays range from minimal to several months, and for most of those more likely to experience longer delays than this, they will generally know, or should upon reasonable reflection know, that they are among those more likely to experience more scrutiny and longer delays, and why. (Many will deny this, but not convincingly.) All that is generally required is an updated clearance, which may cause some delay but usually not much.
As for longer delays than the routine updating of the clearance:
While home country makes a difference, as you also observe, and indeed some countries raise more issues, it is clear that many applicants from such countries do
not encounter significant delays. My guess is that the particular region of the country can make a difference.
But what probably makes the most difference is the nature and extent of travel abroad since becoming a PR and particularly in the last four or six years. Travel since applying is also a factor. The immigrant from Somalia or certain parts of Pakistan, for example, who did not travel to his or her home country, or that part of the world, since becoming a PR, is far less likely to encounter any delays related to CSIS checks than the individual who has regularly visited, or especially one who has resided for a period, in his or her home country since becoming a PR or in the last four years or so.
The more the applicant has been abroad, the higher the risk of elevated scrutiny, including potential referrals to counterparts abroad requesting local inquiries. The latter tend, so far as can be discerned, to result in the longer delays.
Another more or less obvious factor, in addition to any direct reason for there to be a security concern for the individual, is whether the individual has any family member or business associates who CSIS might have identified as either directly involved in activities raising some concern or who in turn have been associated with someone else who has.
Delays can range from minimal to many years, depending again on the individual and the reasons for further inquiries. In formal cases I have seen some take six or eight years. But some relief has been given by the Federal Court, in some cases. At least one Federal Court justice ruled that CIC (then, now it is IRCC) cannot just make the referral to CSIS and sit on it until CSIS acts, that CIC has an obligation to timely process the application and thus may need to make follow-up requests for CSIS to complete its checks. That would be accomplished by pursuing the path leading to Mandamus, and generally it seems (although there is no actual time line) the case must be in limbo for years before this recourse is available.
There are of course special circumstances raising more concern, which might not have been fully examined in the CSIS background check attendant the process of becoming a PR. One example in the formal cases was an individual who worked for an aid agency, as a doctor, during one of the conflicts in the Balkans, and after this individual became a PR, long after leaving the employ of that aid agency, that aid agency subsequently was identified as a potential supporter of a terrorist organization. I do not recall how this case was ultimately decided, but in the meantime the individual's citizenship application was on hold for many years.
But again, for the vast majority of applicants, there is merely an update needed for the CSIS clearance and it is no big deal.