I believe the issue is, unfortunately, that the actual IT infrastructure for ARC is based out of an Amazon Web Services facility in Montreal (can''t say 100% the actual card scanning is handled in Montreal, but myarc.ca certainly is, so seems like a fair bet). It takes time to relay a signal all the way across the country and then be sent alll the way back.
I think this is also an issue with some other online services that just feel glitchier in Edmonton than other cities (Lime I suspect is affected by the same issue for example). Edmonton and Alberta generally just doesn't have that much easily accessible IT infrastructure for companies to tap. I recently needed a server for a personal project I was working on and really had to look for a provider here in Edmonton (went with Net Know, would recommend btw). The difference between a server in town vs. one in Vancouver, Toronto, or Montreal where most Canadian web services are based is night and day as far as responsiveness goes.
Yes, this is an issue. Today, I tried to tap my Ard card in LRT station (Exiting) and it did not respond like after 5 seconds. Then I thought the machine was broken and I went to another. Just I was tapping my card on another machine, there was a "beep" sound from the original machine! This means the delay is outrageous. Finally I ended up "exit" and "entry" again. I need to tap again to have an "exit" again.