I have the same problem with sound - it was working fine then suddenly nothing. No activity in the level meters in the mixer or the Halion Sonic SE window. Have selected the correct device in device setup, have done the Play > Apply Default Playback Template which reset Halion, but still no sound.
I’m not aware of having changed anything between the working and non-working versions.
On previous occasions when this has happened, I’ve had to create a completely new project (which then works) and then copy and paste the data across.
iMac i7
Apogee Quartet
MacOS Sierra