Hi Rich_Art - it's possible that the filleter doesn't know how to handle the patch area at the very top, but you've also got a different problem there in that you've previously filleted other edges that are running into the same area that you want to do now:





So because of that you've got a situation like this where you're only trying to fillet just this edge on the box example here:



That will confuse the filleter because by selecting only that edge and not the one above it you're telling it to try and open up a hole in the model something like this:





So when you've got something like that you need to select a longer range of edges including the one made from the previous sharp-cornered fillet like this:



Then the filleter will be able to try to put in a fillet like so:



So in order for the filleter to have a chance with your shape there, you will need to select those little tiny edges on the bottom areas where you've had that previous sharp-cornered fillets go.

But having stuff like some partial fillets placed with sharp meeting junctures in areas that collide with more edges that you want to fillet is not so good - it's better to do the filleting of such thing all in one go when the edges are interacting with one another like this - doing it all in one go allows the filleter to classify the places where things collide together as needing corner patches in it - by doing a sort of partial fillet before hand like you've done here the filleter now needs to actually consider the previous little fillets on the bottom and process them as things to construct new fillets between so it makes things more complex for the filleting if you do connected edges in separate batches like this.

- Michael