Did you get your PR via PNP and land in another province or something like that? I think you should not ignore this interview request. You should try to find out what it is about. Send a letter to the local CIC and explain to them that you are outside the country and will not be returning soon. Ask them what the interview is about, if you can do it at the nearest embassy or through the phone or clear something up by mailing some documents or if they can postpone the interview until you are in Canada again.
No. I obtained this PR via the skilled worker route by applying from my home country. I had thought that this was pretty straightforward, and since I have been granted the PR visa, and have landed and activated the visa, I can't see how there could be any problem other than something related to the production of the actual PR card?
Additionally, the letter highlights the 180 day time limit to "provide required elements to produce a permanent resident card in Canada", failing which one would need to pay $50 and reapply.