This is an odd one. The quest was changed to require a different/newer version of Von Leon that has 700m HP (instead of 550m) and gives a tenth of the exp. Nexon changed it in v142. Does anyone know anything about this?
Based on what I've managed to google, GMS introduced a new version (Easy Mode) of certain bosses with Von Leon being one of them. This might be the reason why the quest requires a different/newer version of Von Leon (Why the Easy Mode having more HP is beyond me though but the EXP it gives checks out)