What I find is, when I first load the Real-Time activity page, I then immediately click the browser's Reload/Refresh button, and that often prevents such problems for me later.
I use Firefox, but have not tried this in other browsers.
don't know if this is a specific bug with the system; or if it's a bug within my browsers (both Safari and Chrome), but it happens often when I respond to a post, then try to return to the real-time activity page
"We're sorry, but the page you requested could not be found."
"If you got here by typing a URL, please make sure the spelling, capitalization, and punctuation are correct, then try reloading the page"
It gets really frustrating when one has to try and reload the real-time player after every post