Since 6-8 days, or maybe even longer, I notice that the achievement dialog doesn't always load correctly. It doesn't matter on which Stack Exchange site I am, or which browser I use; I keep seeing a spinner for 5 seconds and then it just disappears. At the same time, opening the achievements dialog in the Stack Exchange app works fine; there are also moments when it works on the main site too.
This morning, I could reproduce it with the Firefox developer tab open; the XHR call to
achievements seems to be running into an error:
There are no details mentioned on the error page, the HTML of it is here. Other dialogs in the top bar (in particular the Notification Inbox, which was mentioned to be buggy as well in the suggested duplicate question) work fine.