On other Xenforo forums I've used (and there have been several), the alerts at the top continually update as long as the window remains open. I've noticed that on this site, this very rarely happens. Often the "Alerts" button has no number on it to show how many alerts there are, but reloading the page reveals that there are alerts there. This seems to happen every time for me. I'm not sure if it's deliberate (to reduce load on the server of all the browsers checking) or if it's a bug somewhere, but I thought I'd report it just in case.
Mine seems to be working *I think*. Like this morning, I think I had 11 alerts? But it doesn't always update until I refresh or click on another page.
That's what I mean. The alerts don't show unless you reload the page, or click a link to a different page. It happened just now, but this time instead of reloading the page, I clicked the Alerts button. I could see all the new alerts in the popup even though the Alerts button didn't have the number indicator on it.
It worked for me though. I was leaving a comment in the workshop and a little thing came up in the left bottom corner of the page and said I had a new alert (for what you posted). I think it's a hit or miss thing.
Interestingly, I just 'liked' a post, and it immediately made the alerts show. I wonder whether doing something else on an existing page which triggers a callback to the server (which in your case might have been the draft for your comment auto-saving) and this triggers a check for alerts. While I know how Ajax stuff works in client-server communication for web software, I don't know how it's implemented in Xenforo. In any case, this doesn't seem to be normal behaviour for Xenforo judging by other sites I've used. It's not a major issue, but it would be nicer if it worked how it usually does.
I don't know what the hell you just said, but I'm going to nod and act like I do. I'll come back if I notice anything else about it. I really do wish there wasn't as large of a delay as there seems to be sometimes.
If I'm not mistaken, I sometimes see the "You have X new alerts" popup (lower left of the screen) when I go to a WF tab. However, it does not always happen and I often refresh the page just to make sure I have no new alerts/PMs. I haven't really given much thought about it before, but it does sound a bit weird now that you say it. Given that we usually only have 200-300 members visiting daily (+ bots and guests) I don't think it would put too much strain on the server to poll for alerts every 15-30 seconds (although I don't know how much bandwidth the server has).
I don't think it should be too burdensome, but as you say it depends on the server. Also, I don't know how Xenforo handles the alerts. There are some push notification technologies in web browsers now, which would mean it wouldn't have to poll every x seconds - the server could tell the client when there's a new alert. I don't know if Xenforo does this though.