Add launcher to panel

Sometimes my desktop opens with panel items missing even though I can see it in

~/.config/mate/panel2.d/default/launchers.

Even though the item does not appear on the panel I can see it in the dconf dump and, weirdly, If I add that same item as a new item then I will have two instances on the panel!

The panel/add item dialog will not accept the filepath.

How can I ask the panel to add that launcher?