Check the nut that keeps the tool arm in place, keeps it from sliding forward and backwards....its probably loose, figured that one out the hard way as the same thing was happening to me
"If you're arguing with an idiot, make sure he isn't doing the same thing."
Maybe the cutter shaft is binding up? Try tightening/increase tension on the spring on the left side of the carriage (to the left of the red control handle) that controls depth of cut.
Is your workpiece centered on the lathe? Is your template or original locked -in tightly?