Respectfully, the fact that you even need to type this post shows that the process is an utter disaster. I have no idea how the airport operations work, nor does any frontline YVR or CATSA employee know, nor is there is any signage explaining it. All I know is I go to the airport, I get shepherded through endless boarding pass checks and re-checks (staffed by people who cannot explain what I am even lining up for, nor where this pathway will take me, and sometimes must run after me because I walked by while they were staring at their phones), elevators, escalators and hallways... only to end up getting spit out right into the landside area of the airport! 5 times and counting this year.

When the process works, I will not have to know or care how YVR airport operations work. I will simply be able to follow clear posted signs that do not change by hour of the day and day of the week as in every other major airport on earth. It will not rely on someone personally waving me down and directing me in contradiction to the actual signs, leaving me to guess if they actually know where they're directing me since they are never able to explain it in complete sentences. It will not involve contradictory instructions from employees standing within arm's length of each other.

One day this system may work. It does not today.

The thing about construction - especially during times of rapid expansion fuelled by ever-increasing passenger growth - is that it can create temporary disruption to normal and expected flows and routing. As fast as YVR is growing, the ITD process as described above does not change by the hour or day - the same process has been in place for a year now and is not set to change until the new under-the-roof transfer corridors are completed. It's one of a hundred projects underway at the airport, and one only recently planned, given that CBSA rules are constantly evolving. I'm not sure how elevators, escalators and hallways become involved; once descended from the dual-escalator beside the waterfall, the path is flat and open.

I'm very familiar with the route, having the benefit of being able to walk it at any time I choose, whether or not an actual arriving passenger. Putting myself in the shoes of a traveler unfamiliar with YVR, or even a casual local traveler, I can appreciate the possibilities of missing the required turn, particularly during a busy arrival crush. I can't speak to the exchanges any individual has had with the Dexterra staff that are tasked with directing connecting passengers, but I can assure you they are capable of complete sentences and are very familiar with how each traveler is to proceed - arriving or connecting - from any given flight. Unfortunately, distraction and staring at phones is a symbol of the modern age and is not limited to people in YVR.

I see thousands of passengers each day stroll onto the ITD buses and emerge minutes later on the domestic gates, having saved themselves from the steps of baggage claim and re-checkin. Some seem to fall through the cracks as evidenced by your experiences, although I'm surprised to hear of an FT devotee finding themselves landside after having missed the directions for the fifth time. I'm not sure how the rest of the busloads of people managed to succeed.
The worst possible outcome is a pretty trivial one: you emerge at the international arrival hall and walk up the escalators to Level 3 and down the concourse to pass through the C Gates security to catch the domestic connection. It's not as if one moment of inattention can find oneself standing bewildered in a back alley with the dumpsters, the door clicking locked behind you.

Give me a heads-up the next time you pass through. I can stand at the base of the waterfall, smile and point you to the bank of awaiting kiosks.

Thanks to this thread I now know the proper process to use ITD OSS at YVR.

Today, since the four red vested employees whose sole job it is to direct people to OSS were chatting behind a pillar instead of unlocking this process for arriving passengers, I was the only one from my flight privileged to use it. Got a private bus and everything.

Can someone please explain what the terms OSS and ITD? I feel ignorant.

OSS = One Stop Security (Don't Re-clear Security)
ITD = International to Domestic (Baggage Checked Through)

For one to be eligible for OSS, ITD must happen, but people on some forums are saying that OSS is CATSA business while ITD is CBSA business.

Reading this thread I've realized that in spite of my thoughts, my transit in YVR might not be as convenient as I expected
In early September I'll arrive to YVR from TPE on BR flight (at 7:25 pm) and then will have AC flight to YYZ (at 10:30 pm). Both flights will be on one ticket and in J (if that matters). Could you please tell me, if shortcut between international and domestic terminals which was mentioned by [MENTION=4519]ACfly[/MENTION] in first post still exists and how can I find it? Is it available also for residents of countries other than Canada (I'm Polish)? I'd like to get to domestic terminal as quick as possible in order to spend some time in AC MLL (as far as I understand, it's not possible to use AC lounge in international terminal after arrival?).