I have to say, that I must be one of the lucky ones.
Unfortunately, AC's IT issues affect me about 50% of the time and I have tons of issues doing OLCI. That means that at YVR I often have to head to priority checkin. They are always super courteous and I have only encountered one issue there in the past when they couldn't find my flight....and that was not their fault, I had booked for the wrong day.
That one time they immediately made some changes and got me on standby for the flight that I wanted. Somehow I even got upgraded at the gate to J, and I did not see one change fee or anything. They cancelled my later flight and no extra charges.
I was pleasantly surprised.