My custom games against ai start normally but gradually sounds stop playing. after 5 minutes no sounds except music can be heard. No explosions, building sounds, unit movements, complete silence. I've already disabled all other sound devices except the ones to my head phones.
No sound after 5 minutes
@binaryman You should go to Windows key > type: Control Panel > Open > Sound > Playback > select the Device you use > Configure to ensure that your sound device is set to Stereo then look in Properties to make sure that all Enhancements & Spatial Sound are Off. After you've verified those settings, usually a simple Restart or Shift+Shutdown (not just Shutdown) of your PC will resolve the sound issue.
If your headphones come with any applet/program, then you may want to disable that & try using the headphones without it. Similarly, if they use a USB or Bluetooth dongle to connect to the PC, see if you can connect directly without the dongle.
If that doesn't work, then you can have a look at this thread for further troubleshooting: https://forum.faforever.com/topic/4084/solutions-for-snd-error-xact-invalid-arg-xact3dapply-failed