Hi Brian, this is another instance of some misalignment between the arc corners and lines.

Here's what I mean - on the outer profile, I turned on control points:



Then I zoomed in closely to the area circled above. There you can see that it is arranged like this:



The rounded corner part is not tangent to the line it connects up to, there is a shallow angle there. Shallow angles like that will create difficulties for the filleter, it means the filleter cannot calculate a single smooth piece marching around that corner, instead it has to come to a corner piece and try to fill in the corner.

If the corner was tangent to the line instead of having a crease there, it would be easier for the fillet to be calculated.

To be able to fillet the end result, you're going to need to be more careful when you place those rounded corner parts in - they can't be just eyeballed to be within 4 or 5 degrees of being tangent, they need to be snapped on to be nice and smooth there.

One method that may be easier for you is to not try and manually draw the corners at all, instead use curve fillets to create them for you, that will ensure they are nice and tangent automatically.

To do that, create your outline with sharp corners on it like this:



If they are separate pieces, select them and use Edit / Join to make them into one curve.

Then select just that one curve, and run Construct / Fillet. Some points will appear at the sharp corners, and you can select which ones you want to be rounded:



Then pick a radius, just like you do for a solid edge fillet, but when applied to a single curve it will round the corners of the curve:




Placing rounded corners into your curve using this method will guarantee that the corners are all tangent with the neighboring line segments, that will avoid a lot of filleting problems later on.

- Michael