Make sure your pathnodes are close enough placed on both of the sides of your debris, with a maximum grid space of 128 placed from eachother.
Have you added the following kvp to your debris?:
If not, add it.
Is the box "DYNAMICPATH" selected if you open the entity window using "N"? (This should be selected if you added a spawnflags kvp tho.)
If not, select it.