I had a similar issue this month for Iberia flights issued by BA. Called Iberia multiple times for seat requests; they confirmed my Sapphire status and assigned seats with no charge. The next day, the seat assignments had gone.
Eventually got a knowledgeable Iberia agent (they are few and far between!) who took out my FF number, then re-entered it, assigned the seats, and bingo - they stick!
Maybe similar problem with your QR flights? Try getting QR to delete the Sapphire FF number, then re-enter it.