Hey, guys. I also had problem with this achievement and did what Demon596 told. I got the achievement but at the wrong time, it popped on Zilo Beast, after I got my 5th mini-kit. So yeah really glitched achievement.
Some extra information: I never left the starting place on the hub, didn't even build the elevator. The extra levels remained untouched. Game crashed once during story on Grievous route (still much better than the 6 crashing I had on my first playthrough). At one of final levels, I messed up and got 1 mini-kit during story mode, but finished it anyway instead of exiting and trying it again. This same level I had to play twice on free play because I missed two mini-kits (again, finished the level instead of trying all over again). And I always, always, played the levels until the end rather than save and exit.
Hope my story helps anyone trying to get this achievement or even figure out what causes the glitch.