After you make sure that there is no error displaying on the console, this should return your max value:
- $gameParty.leader().maxlus
Oh, got it. These parameters are like HP/MP. As so, you need to set their value at 100 on the class note tag you used.
It's like on the class editor curve, when you set an HP value there, the character will start with that HP value: 100/100 But if he loses 10 HP, it will be like 90/100. So, set on the note tag the lus value to 100. If you want the current(not max) value to start at 0, then you use the script call on the help file to set it at 0.