This might be due to the sound service suspend-on-idle.
More info:
If you still have issues with audio cutting out, you can try editing /etc/pulse/default.pa.
Change:
### Automatically suspend sinks/sources that become idle for too long
load-module module-suspend-on-idle
To:
### Automatically suspend sinks/sources that become idle for too long
# load-module module-suspend-on-idle
And edit /etc/pulse/system.pa.
Change:
### Automatically suspend sinks/sources that become idle for too long
load-module module-suspend-on-idle
To:
### Automatically suspend sinks/sources that become idle for too long
# load-module module-suspend-on-idle
Then issue:
pactl unload-module module-suspend-on-idle