I had the same problem a month or two ago and wrote about it here, so it might have been my post you are thinking. I ended up changing the browser for a while.... and after some time it just started working on the other one as well.
I tried it in all three of the browsers I have installed. Same result every time. As I said before I haven't had this issue on any other website, so even if it's intermittent it's at Upwork's end.
I use Opera browser, and my Back button has a dropdown list showing all the previously visited pages in a tab. It's useful in case I want to go back 3 or 4 pages, rather than just back to the previous page.
The point is, when I go to the Message page, and then click on the drop down list to go back, there are TWO pages between where I am and the page I came from. So when you click on the Messages link you go first to a page called "Messages - Upwork", which redirects you to https://www.upwork.com/messages/rooms/ , which redirects you to the Message Center page (room) you see.
So clicking on the Back button takes you to the page that redirects you to the Message Center.
Probably doesn't help you very much, but that's why you can't back out of the Message Center anyway. I don't think they're going to be changing it anytime soon.
Thanks for that; it was very useful. Two of the browsers I use - IE11 and Firefox - have the same feature. Sure enough, from the Messages page there are two more pages between where I am and where I was one click ago, and one of them is a redirect that I can't click back through.
So the Message page is indeed broken, and it has nothing to do with my cache or browser. Much to my unsurprise.
This functionality has been fixed and you should now be able to navigate from the Messages by using the browser's back button. Please, let us know if you have any questions or further issues.