So I have both Cubase Elements 8 and 9, and was constantly frustrated with the program freezing when I did an Export Mixdown in Elements 8 - this required closing Cubase in the Windows task manager.
I have seen other reports of this around, but usually in reference to only happening when something else in particular was running (Loopmash, etc).
This happens to me with NOTHING special running.
So I upgraded to Cubase Elements 9 in an effort to escape this problem…
AND IT’S STILL THERE.
Any suggestions? 
Are you sure it’s frozen and it’s not just the progress bar not showing anything?
If it indeed is freezing, I would have a look at plugins and drivers, maybe try realtime export.
I’m absolutely positive it’s frozen… I can go away for an hour and it still won’t finish.
I have tried disabling ALL plugins and VSTs I have before a mixdown, and it still does it. Not every single time, but enough times to seriously impede my workflow. I’d say probably 25% of the time.
And I’ve seen posts in other forums with people having a similar problem. It doesn’t appear to be just me.
Is never actually tried real-time export before… If that fixes the issue with no loss in sound quality, I guess that’s a solution. However, get a lot of clicks, pops and dropouts during normal recording playing. Live recording even sometimes fails completely 
Real-time peak in VST performance is often completely maxed out for me too, despite having a very high spec computer (16gb RAM, fast i7 processor, not connected to Internet during recording, etc).
Has there not been ANY progress on this??
It’s like a year later, I’ve updated to the most recent version (9.0.20 build 209)…and it STILL doesn’t work…