Chrome/Chrome OS Version: Whatever was running on the AOpen Chromebox Mini on December 28th, 2017.
Chrome OS Platform: AOpen Chromebox Mini
Network info: not sure, probably doesn't matter.

Please specify Cr-* of the system to which this bug/feature applies (add
the label below). ← I don't see a button to do that anywhere.

Steps To Reproduce:
(1) Set up a new Chromebox AOpen Mini.
(2) Open Chrome and go to Google Calendar (calendar.google.com).
(3) Select "Menu", "More tools", "Add to shelf" (or something — I had the French version of the system so I'm not sure what the English menus are).
(4) The icon appears, with today's day number on it.
(5) Wait until tomorrow.

Expected Result:

The icon changes. More generally, favicons are updated somewhat regularly. This would also be useful for websites who display additional information in the favicon (like number of unread messages)…

Actual Result:

The icon stays the same. Favicon changes are never picked up, even if I open the page later in the same day.

How frequently does this problem reproduce? (Always, sometimes, hard to
reproduce?)

Always.

What is the impact to the user, and is there a workaround? If so, what is
it?

It's kind of ugly to have a big icon with a random number on it, and that number being completely irrelevant (except once a month, heh). I didn't find a way to change the icon to something without a number, either.