Replies submitted, but never gets confirmed in browser

Is anyone else seeing slightly curious behaviour?

I submit a reply, and my browser (Chrome) submits it and the spinny ball in the V:EKN tab spins round telling me it's submitting the response. And it just stays there doing that. In another tab, I can see the response has been submitted (because the thread has been updated and I can see my reply), but the other tab just continues sitting there looking like it's still submitting without getting a response from the webserver.

I've only seen this behaviour in the last 24 hours or so where, to the best of my knowledge, I haven't changed anything at my end.

Getting the same thing. Also using Chrome.

*poasts with chrome*

works totally fine for me?

First time ever this happened to me just a second ago.

Stopped the endless spinning made pressed "submit" again and was told "Error. A duplicate message" or something to that effect.

EDIT: Apparently it is a bit random, since a minute later when I posted this, I had zero problems with it. So the above has happened to me only once so far.

Using Firefox 59.0.3 (64-bit).