Google chrome not displaying alert() popups for one site

Not tested but if you have the problem again I think opening the site in an incognito window will reset the dialogs.

Edit: I added this answer which worked for the Chrome build as it was. Updates might have rendered this unnecessary (appreciate not to be marked down!)

You don't need to restart the browser. Just close the tab and reopen it again. It does not need to be Incognito.