Using two USB Yeti Microphones to record a podcast with Garageband

When aggregating 2 mics via OS X Audio MIDI have you ever ran into an issue that only one of the mics is recording even though you have combined them? And when recording each mic is on their own channel in Garageband (using the most up to date software)? Running Yosemite. I've tested on both same issue. Note both mics have different serial #'s.