Since one of the Ps is physical presence, it is obvious that it is verified by/with CBSA. So, what is part of the normal processed is not a "delay" per se. I'm going to assume that all presence claims are checked against CBSA data, but there may be especial scrutiny where the days present reported by an applicant do not match the CBSA total -- this scenario might trigger a secondary check even if the legitimate total is still above 1,095. (Hence why IRCC recommends not cutting it super close to 1,095.)
Delays are mainly driven by caseload burdens for specific offices and a lack of FIFO.