Same issue in 2024
In my case they sent it to a vacant site address, I was told to wait for 6 weeks as well by IRCC and they suggested by law Canada post must send it back to sender if its undeliverable , In addition he mentioned sending is faster and return is slower because it moves through different departments and procedures. The agent on call with me helped me to correct my address on their end, He further advised they receive numerous calls everyday for wrong address delivery. I also called Canada Post and they advised because there is no tracking id they dont know where my mail is and will be returned to IRCC.