Irregular Fillet

Hello, I’ve been trying to learn Rhino for the past few weeks while doing some experiments with shapes. I made these two objects with that “bevel” inside, one using Sweep 2 Rails (right) and the other one using Loft (left), however, I got two results after applying a small fillet. The Sweep one has some irregularities while the loft one is okay.

In the picture below you can see that the curves have some irregularities, they’re not straight.

In this one (using loft) it’s perfect and I could use that.

But I want to understand why did that happen… Why using Sweep 2 Rails didn’t work.

Hello - look at the plan view of the sweep - my guess is the isocurves are skewed - you can use ‘Add slash’ in Sweep2 to force the alignment to the ends of the corner arcs. Post your file…