The current 3/5 rule is a strict physical presence rule, like the 4/6 rule which governs applications made between June 11, 2015 and October 10, 2017.
This is not about IRCC (or CIC) policy. This is what is prescribed by the statutory provisions governing the grant of citizenship for adults (who are not otherwise entitled to credit related to Crown Service). IRCC has no discretion to waive the presence requirement.
Thus, as others have responded, the application will be denied if the applicant falls short of the minimum (which is 1095 days within the preceding five years for applications being made now) even by one day, regardless the reason.
Some confusion about this is entirely understandable, since there are many applicants with a case still in-process for whom the old residency rules apply, which may allow the grant of citizenship notwithstanding absences and total physical presence less than 1095 days (within the preceding four years), and of course there are scores and scores of naturalized citizens who were granted citizenship (under the old rules) who fell short of the physical presence threshold, and there have been some relatively recent Federal Court decisions upholding approval for a grant of citizenship even for someone who fell quite a lot short. Those residency rules, however, are only applicable to applications made prior to June 11, 2015.
This is significant as well because it illustrates two important observations:
-- the importance of a buffer, a comfortable margin of extra days over and above the minimum; IRCC is now actually explicitly encouraging prospective applicants to wait to apply only after they have extra days above the minimum
-- always exercise caution in considering anecdotal reports, that is, reports in the form "this or that worked for me . . . " because many times there are reasons why what worked or happened in one case does not indicate what will work or happen for someone else . . . whether that is due to the law or rules changing, as they have regarding requirements for citizenship, or more often because there are other factors in play