You need to leave off false just type "bucks.lock_all_perks_for_bucks_type 40962 " without any quotations if you do this it will permanently remove all weakness points from your vampire (make sure you have assigned all the weakness points first otherwise it won't work), but you can ADD back the weaknesses using the equip trait cheats (https://www.reddit.com/r/sims4Cheats/wiki/vampcheats)
It's time consuming, but you'll be able to give your vampire 5 weaknesses instead of 6. Then you can refund it normally later once you have ranked up if you want to switch it around (though can't guarantee it won't bug out again!). Or you could live with the 6 weaknesses until you are a high rank then do the cheat. I am not sure why more people don't know about this, but I found it tinkering around and it's the workaround I use when I want vampires with varying amount of weaknesses. If you leave off the false it will take all your weakness points and you can assign them however you want by equipping them (through the cheat menu in game).
