FilletEdge issue (rhino & grasshopper)

Is there a way to know why this edge doesn’t work with FilletEdge ?
I want 5 mm radius but anything else failed also.
It doesn’t work either in Rhino.

FilletEdge_Issue.3dm (65.8 KB) (5.0 KB)

Hi -

If you remove that small cut in the upper surface, it will work as you expect.

Ouch ! The devil is in the detail.
Thank you.