I'm not sure if I am hallucinating here, but doesn't Houdini usually highlight any unshared edge when the view 3d island boundaries button is toggled in the viewport? It seems to only be drawing the profile of the shape? Also, I'm getting a similar behavior with the display uv island boundary toggle as well.

Attachments:
screen1.png (1.7 MB)
screen2.png (2.3 MB)

seems to work fine here 22.0.408

Attachments:
view_3d_boundaries_H22.0.408.gif (36.1 KB)