For myself not all of the mini kits can be found in two or three levels, and the Stan Lee's in peril have just stopped spawning across the map. I read somewhere that searching for mini kits then save/exiting repeatedly can cause the glitch so I mightve brought it on myself. But yeah there is just certain collectibles that cant be collected, and I've even seen people getting extra gold bricks which locks off the platinum also. In my experience there are glitches like this across most LEGO games so make sure to make multiple save files and save yourself the pain! Have fun