When putting inserters behind cargo wagons you can still see them, to recreate this just put a few wagons horizontally and then put inserters behind them.

Im sorry but i cannot fix that bug, it's a game bug that has been there for a long time.. even the staff from factorio has anwsered it and they said the following
"We are aware of this problem but it is not solvable easily until we change factorio to 3d which will not happen anytime soon"
what i would recommend is either place it south instead of north or get a mod that can help with it.. or just try avoid thinking of it