I think that the location of the documents check is the crux of the matter. Some people with previous experience on other airlines when traveling with hand luggage only, have been able to online check-in, go through airport security, then have documents checked/verified at the gate area. Air Asia however, does this verification and stamping process at their check-in/counter area, well upfront in the sequence even if you check in online with them. I'm actually a little surprised that Air Asia even allows online check-in on itineraries where passengers need visas. But since it's possible, one needs to be aware of the Air Asia drill, and not get too smug with online check-in and inadvertently skip this step, only to get bounced back at the gate.