in houdini 19, i create a grid (4 points) then add group node and set the group name : above . Then I add a knife node and position the cutter so it cut the grid in half. then inside the knife node, set group to : above and also turn on the 'create group' and set the above plane group name to 'above' (same as the source/input). The knife works fine.

But in houdini 20.5.487 , it works only if i turn OFF the 'replace existing' (in the output group section). if it's ON then the knife won't work. is this a bug in h20 ?