Can you swap the lefts with the rights to even them up? IIRC, there's no spring clips so they should be able to be left or right.
I had one set of Hawk HT-14's that wore on only the inner pad of one front wheel. The pads before and the pads after didn't do the same thing.
One thing I wonder about is could it be possible that the good side got a little grease or something that made them work less. Did you feel anything in the pedal/wheel?