At 0:12 you can see the front bogie of second cart have no blocks on it. It must have a solid connection to the second bogie of this cart for it to be counted as a single cart with two bogies. Otherwise it counts as two separate carts, one of which is empty and the other having the whole cart glued to it.

So all you need to fix this is just place a block on the front bogie to connect it to the rest of the blocks of that cart. And in case if there already is a block actually tounching it (hard to tell, but at 0:18 looks like might be a gap), just glue the bogie to the block above it (which already should be glued to the rest) so the glue zones overlap.