You may have fallen foul of the infamous Mamiya TLR shutter interlock. If you press the shutter release a little you can trip the interlock but not the shutter. Result, you think 'damn, should have advanced the film', and do not expose the frame. This can happen if you forget to cock the shutter on the C220, too. The shutter doesn't trip, so you wind on. There are work-arounds for that.
It should not be possible to operate the shutter control with the lens change baffle up, so that shouldn't be the cause.
What lens do you have? There are a couple of lenses that will allow the shutter release arm to move even when uncocked. The 80 f3.7 is the usual one.