I don’t know yet - I suspect it has to do with the singular surface - if I split a piece off near the fillet the trim happens as expected. Also the surface is not G2 internally - only tangent - that may come into play as well. If I RebuildUV in V to be smooth, the trim is successful
I’ll put this on the pile.
The rail has a fully multiple knot at these locations - I guess that is the reason the sweep does not negotiate it cleanly. It looks like it ought to, to me as well - but for now, RailRevolve is you friend here.
-Pascal