I've noticed a strange problem, I cannot get it to occur on all discussions.
I noticed that I'd had two new updates on a blog post, so I clicked on 'show more activity' (I was logged in):
I got a 403 error showing up in the debug. I did a refresh Ctrl-F5 but the problem still occurs. This is with up-to-date Chrome on Win 10.
This is what I see when I click on that error from the debug:
This is the request:
Retrieving data ...