The somewhat recent suspension of Program Integrity (PI) interviews was clearly a temporary measure in response to the Covid-19 global pandemic.
PI interviews are part of the routine process. Prior to measures taken in response to Covid, ALL adult applicants were subject to a PI interview. PDI (Program Delivery Instructions) still list the interview as a mandatory step in processing all adult applications, and it is likely that IRCC is migrating toward resuming PI interviews for all applicants.
For the vast majority of qualified applicants these interviews are mostly a formality, largely perfunctory. To a significant extent they are focused on reviewing the applicant's documents, a verification check, and to some extent verification of identity, current status (no prohibitions for example), and technically screening the applicant's ability in an official language (which is not structured like a test, but is mostly screening how well the applicant understands questions and responds in the interview, which typically involves what seem like casual questions but which really are part of screening the applicant's language ability). For most applicants the interview is very short. Nothing probing let alone challenging.
That said, the range of questions potentially asked is huge. Applicants can be asked about a wide, wide range of matters, including questions about any aspect of the information in their application, but also questions about the applicant's life, current or past circumstances, including addresses and employment and such (not limited to the eligibility period), or about the applicant's family. This is NOT how it usually goes, but how it can go for many. Applicants with nothing to hide have almost zero cause for concern . . . the questions are not challenging or confrontational (with some exceptions for applicants whose physical presence is being questioned), so all the applicant needs to do is SIMPLY and HONESTLY answer what is asked.
Applicants who have been known or perceived to be abroad for extensive periods of time after applying appear to be more likely asked questions about current location and employment, questions related to verifying the applicant has returned to Canada, or questions about when the applicant will return to Canada.
But, again, for the vast majority of applicants, the PI interview is simple, fast, NOT a problem, not at all a problem.