Game hangs when focus lost after some time

Windows
1

When I alt+tab out of the game, after a while the game hangs. The currently it’s running on is

 lock (_d3dContext)
                    _swapChain.Present(syncInterval, PresentFlags.None);

I’ve also got a bunch of these in the output.

The thread 0x5e28 has exited with code 0 (0x0).
The thread 0x4894 has exited with code 0 (0x0).
The thread 0x5958 has exited with code 0 (0x0).
The thread 0x4554 has exited with code 0 (0x0).
The thread 0x4d34 has exited with code 0 (0x0).
The thread 0x3f8 has exited with code 0 (0x0).

Back when we had an IndieCity XNA build, audio playback when the game was unfocused would cause something similar. Beside this, I’m not sure where to begin to find and more and fix it.

This is a x64 build, that is being released on Steam.