Problem cutting a rectangle

Downloaded a box layout, but one of the rectangles cuts from top right to bottom left for the number of passes, then cuts the other half from top right to bottom left for the number of passes, instead of cutting all the way round as all the other box sides do.
It cuts out ok but I cant see for the life of me why…
Close inspection shows everything appears to be in order, marching ants, node editor shows all nodes connected.
Anyone throw any light on it please.
TIA.

A screenshot of the Lightburn settings and workspace would help…