You should ensure that you install the current device drivers for your AudioBox.
Now, Windows native audio programs, like Discord, and others like Skype, can only use a "pair" of inputs. So, when you set to inputs 1 and 2, and you only have 1 microphone connected, you will only hear/stream the mic on the left or right channel respectively.
You may need to use a 3rd party program that can "mono sum" the input channels to both input streams to your software.
Look into VB-Audio and VoiceMeter.