They intentionally made it so those can pass through areas like bars, from what faatal said. It just means updating your base design. That is actually a good thing, though. If you don't need to change your base after they add new zombies, they did it wrong.
So a giant boulder can pass through a tiny opening... makes zero sense. So what's the point of having turrets if switches and relays can get destroyed so easily??? The game is supposed to be a sandbox tower defense zombie game. It's a very bad thing because they only want to make it so people stand in one place with the most OP melee build using the same horde base design. Look at YouTube, people only use two different cookie cutter horde base designs now...