Few days ago, on Monday I believe. That was probably just a new look, because themes got switched, but I assumed forum got upgraded, because things started to look different. I also did not mess with settings, I dont know why it has changed for me
I agree with what you said, the change was your theme somehow getting switched. The only upgrades we've done are on the backend, they wouldn't cause any changes to what members see, and we haven't even done any of those recently.