If you type "disconnect" at the console, are you able to join servers/play demos again?
I have same issue. Tested with playing another demo, it works after "disconnect".
Also I noticed that when after I hold the speed key, playback froze, so I released key, when I pressed it again I got message "==== ShutdownGame ====", but nothing more (I'm pretty sure it wasn't end of demo, but maybe serverside it done playing it somehow). When I tested it again on another map, couldn't reproduce that easy, but seems that message fires off after some time anyway (when I minimalized game window to write down my observations 'couldnt reproduce' [tried pressing key several times, also for longer time], it show off after I maximized it again).
Another thing I noticed: This froze bug happened when I launched game and started some demos, after that I tried playing other demos, and now it doesn't seem to freeze anymore (was able to fast forward for longer amounts of time, until map ends).
Keep hitting the key, or hold it down for a second, lift off, and hold for a second again, etc. Did that for me when I had the bind.
We need a script to slowdown time every second or so. Or maybe just fix bug?