when the iron bars are connected to each other or are in different forms, arrows and other projectiles don't go past the iron bars. In java, if you shoot an arrow from the top and right into the hole where 4 iron bars are connected to each other, it passes through with no problem. In bedrock, the arrows get stuck as if the iron bars were full blocks. The arrow just floats there.

The same bug happens to similar hitboxes like glass panes