While platforms are docked, removing the very first belt that comes after the dock belt's output, then replacing it makes only that connection stop. This occurs without changing the docking ports or controller. It gets fixed after you redock the platform
This is due to the dock belt being updated whenever you place a belt at its mouth (as it automatically changes what direction it's facing to connect with the belt properly), and as part of this, the docking belt has to be unlinked (since if you change the direction of a linked belt while it's linked, the game crashes)
I can see what I can do to improve this behaviour and re-link the belts afterwards, but cases like this will probably always exist, simply undocking and docking again is probably your best bet.
