Similar to my case, I landed in 1997 but didn't stay in Canada , then back to HK until 2016 . In 2016, I wanted back to Canada and tried to use HKSAR and applied eTA, then rejected from Canada immigration when I applied it. So, I tried to apply Permanent resident travel document(once time only) to travel back to Canada, and I was success to apply and got back to Canada in 2017.