TheIt seems like that add on just creates a bunch of extra geometry by default -on seems to have slightly extruded the top faces -are subdivided strangely so the Geonodes is performingeven creating an additional extrusion on topvertex group of only the one already done bytop faces and using that to select the add on. Toextrusion still doesn't fix thisit.
I simply scaledjust ended up scaling the z axis to zero0 and merged by distancedoing a limited dissolve to get all flat facesa single face per island. Seems to work normally nowThen the geonodes set up behaves as expected.
As long as you don't specifically need that extra geo it should be fine right?