Missing passport tends to invite some questions, potential concerns. It is considered an important piece of evidence. And the lack of evidence tends to hurt the party with the burden of proof, the burden of presenting the evidence. That is, the applicant.
But as
@btbt observed, the impact can vary widely. The impact can range from having very little impact,
no problem at all, to causing IRCC to have serious questions or even suspicions.
As
@btbt also observed, in effect, the impact can depend on how strong your case is otherwise.
Standing alone, without other negative influences, and particularly if the margin of presence is substantial and the applicant has a strong work history in Canada, my sense is that there is a good chance a passport lost and replaced nearly four years ago will
NOT be much if at all problematic. This depends, of course, on other factors and how solid the applicant's case is otherwise.
A lot can depend on factors such as:
-- the length of time (within the eligibility period) for which the missing passport could have been used (less is better; more tends toward problematic)
-- when it could have been used relative to claimed presence in Canada (if, for example, most of the time present in Canada has occurred since the passport was properly reported lost, the lost passport is less relevant, less likely to be an issue)
-- any indication of undisclosed travel or signs of travel indicating use of some undisclosed travel document (basically, if IRCC sees evidence that the applicant was using some other travel document, which could be the reported lost passport, obviously that will raise concerns)
-- any reasons for questioning the applicant's credibility
Note, any applicant, no matter how perfect the application, can be issued RQ. It can happen. It does happen. There is NO guaranteed way to for-sure avoid RQ. So, a somewhat elevated risk of RQ is manageable. Just be prepared for it if it happens.
In particular, while RQ is dreaded, for good reasons, it does not necessarily mean it will be difficult for the application to succeed. Moreover, there are less intrusive possibilities, like RQ-lite and a request for just a few additional documents. Not all RQ'd cases take an extraordinary long time. If the applicant timely responds and well-documents the applicant's address and work history, and otherwise provides information and documentation supporting the case, the application can proceed timely through the process to the oath.
Note that not all RQ'd cases are equal: sometimes IRCC is merely doing due diligence in verifying the applicant's qualifications; that sort of case tends to go more smoothly and quickly than, say, a case where RQ has been issued because IRCC has overt suspicions about the applicant's time in Canada.
While there are exceptions (as forum whining well documents), generally there is a reason why applications run into more serious problems. Meaning, if the applicant is qualified, follows the instructions, provides the required information, and especially for applicants with a strong work history, the process almost always goes smoothly and without much delay . . . EVEN IF THERE IS A WRINKLE OR TWO, such as a missing passport (subject to factors such as those referenced above). IRCC tends to figure things out. A lot better than many give credit.
(Caveat: "without much delay" is relative. There seems to be an extraordinary number of forum participants of late who see six months as an extraordinary long process. Many are likely to be disappointed. My sense is that a total timeline of six to eight months is still well within what should be anticipated for most even though some do make it through more quickly, and thus for any non-routine process along the way, any timeline less than a full year would be, relative to the history of citizenship application processing,
without much delay.)
