I’m using Djay Pro 1.4.4, and have always had this problem.
I use an external audio interface, actually 2. And it happens with either a Presonus AudioBox 22VSL or a Focusrite Scarlett 2i4.
When selecting the interface as the microphone input, the microphone only outputs to the corresponding channel/speaker. When the mic is plugged into channel one of the interface, the mic only outputs to channel one of the interface. Plugging into channel 2, only outputs to channel 2. So the microphone output only ever comes out of 1 speaker at a time.
Anyone else have this issue? If so, does anyone know if it’s fixed in Day Pro 2?