This game is basically unplayable because of the glitch that makes the robot car things stop being recognized by the game and go to the corner, because they are unkillable and you cannot beat the level until they are dead.

Ohhh thank you so much, yes it seems to work now without that bug.
I know how annoying it is to garbage collect unneeded objects without removing the references to the wrong ones. For me, I've had trouble because I kept my enemy objects in Arrays (although I suspect linked lists would be better as I add and remove enemies more than I use random access on the lists) and when splicing the killed enemies or the ones off the screen from my arrays as I cycle through them, my counter to hold the index of where I am tends to get messed up when the Array length changes after a splice and elements get shifted and my index counter gets out of position causing me to skip over objects or delete the wrong ones. So I've also had that sorta "hanging" object glitch were a displayed object is no longer "known" to the program at least in part (as in this case it still needs to be destroyed).

On a side note, Isn't 100 fps a little overkill

Maybe the easiest way would be to copy the objects from one array to another array. This way even be the fastest solution if you remove 3 or more objects each time. But speed may not really matter if the number of objects is low.

I don't know though, because even if you have, say, 8 objects in the array, you're still creating a new 8 object array each frame. So that's 30, or 60 times a second that a new array is created (even though it is short). That might be sorta slow.