And even some agents are stricter than others at the very same ticket counter/gate. OP - you may get more Air Asia user experience in the given airline forum where I've alerted a mod to request a move.

I've only had one flight on Air Asia, REP-DMK, so can only offer one data point. The agents didn't seem to be going out of their way to size carry-ons. But my one experience shouldn't be taken as an assurance. IIRC Air Asia has a weight limit on carry-on bags as well, I didn't see anyone have theirs weighed but I heard from a couple folks that the carrier sometimes does weigh them.

As noted above it's hard to generalize, though myself and others on FT have noted anecdotally that regular sized backpacks (i.e., not the camping style packs) generally are less likely to attract an agent's curiosity than rollaboards, particularly for airlines that are concerned with weight limits - but again can't guarantee.

Best advice as the prior posted noted, is to just be prepared in case you are challenged and the bag doesn't fit. I usually keep my valuables and lithium batteries together so I can easily pull them out of the carry-on in case I'm forced to check it for some reason (though that's rare as my backpack is within most limits and fits under most seats, but you never know).