Spacebar does not play... then manually pushing play doesn't play

I may have had a similar issue. Clicking the triangualar plkay button or hitting the space bar did absolutely nothing. The audio hardware was set correctly. But when I switched to the built in speaker... it worked fine, and then when I switched back to the headset I was using previously it worked fine.. go figure... 

Preferences > Audio Hardware > double-check it's not still connected to an external device / output no longer connected.

It sounds like the behavior when the audio device communication is partially interrupted in some manner that doesn't trigger the standard OS library notifications.  Generally, it means Audition is no longer getting a word clock signal from the audio hardware, but hasn't yet been told that the audio device is not accessible by the OS.  The "word clock" is sort of a digital pulse that synchronizes an application's IO with the hardware data stream.

So, let's find out what's happening and why. 

1. What audio device are you using?  Just the built-in microphone and output, or do you have one or more separate USB or Thunderbolt devices connected?
2. Are any other audio-focused applications running at the same time as Audition when this occurs?
3. If you restart Audition when this happens, is playback working again?
4. The next time this happens, please click Help > Reveal Log Files in the menu bar and send the most current files as an email attachment to audbugs@adobe.com  and we can take a look at what messages Audition is logging and continue troubleshooting.

Thanks

When it freezes, does Audition actually crash, or does it recover eventually? Makes a difference, because if it crashes it will generate a crash report which will almost certainly give a much better clue as to what is happening.