What type of PR visa did you apply for? Spouse? Common-Law? Do you live together? I would think that if a cpl have been living together for 4 years CIC would not need proof of previous chats? Me and my partner did not really chat a lot using any APP's or even facebook, if we did it's all lost now or we did not keep most conversations because we have just decided that we would like to go in Canada and start our life there in recent months.
You and I are in the same boat. Common law partner, lived together 3 years now. Although currently visiting Canada.