Everytime the boxes in the station switches it misses one spot.
I believe that's the reason why many players (aka.: some youtubers I watch) think they're unreliable,
this single line will always make 4 full belts of extraction develop spotty belts on the end of the line
and cause a full delivery of 4 belts of shapes to overflow the trains,
no matter how many trains you place, the stations don't deliver 4 belts.