There is a forum here called permanent residency obligations:
https://www.canadavisa.com/canada-i...rd/forums/permanent-residency-obligations.11/
Short form: any time you are out of compliance, when you are examined (like arriving this summer), they can look into it and issue a report (44(1) report for the section of the law on this). That effectively declares you inadmissible - subject to appeal - which will eventually result in losing PR status if appeal is not won (or if not appealed, I believe in 60 days). "Inadmissible" at this point does not mean you won't be admitted - you will be admitted to Canada and are a legal resident until the PR status is revoked (eg appeal lost or not appealed).
Note, they may not issue the 44(1) report - it's possible they could just warn you again, or not even ask a question about it. Or they could examine and decide to let you off for eg 'humanitarian and compassionate' reasons(if you have any be sure to mention them). It's unlikely they would wave you through with nothing, though, since it's probable a note for file was made last year (to examine you on subsequent entries); that said, I don't know this for a fact, it's possible the border officer last year was just being nice to warn you of potential consequences (which you ignored for another year) and didn't bother making a note to file.
Technically you could leave and return while in appeal but more complications would ensue, and not remaining in Canada would definitely reduce chances of winning appeal.
The card's validity will be revoked with the PR status.
Important note: PR card and PR status are two very different things. Lose your card, and you are still a PR. PR status revoked - card will no longer be valid despite the date - outsiders would not know but eg the PR card would likely no longer work to board a plane, for example. Card itself does not say anything about your compliance with the residency obligation. Being 'non-compliant' on its own won't stop you from getting on a plane.