- One reason can be wrong adjustment of gear shift buttons during long time. If there was no play underneath the button in the pushed position, clutch may not have engaged completely. With the consequence, that there was too high load on the edges of the clutch and therefore the edges got rounded.

- Another reason may be too high side play of the chainring. Please check this play carefully and adjust the self locking nut on the left side to eliminate this play. (-> I.4.