I suspect one aspect of the problem may be that one of the lines coming into the corner is an arc, not a straight edge. Depending on which tool you use to draw the arc and where you start the arc, this can confuse the tool because it can’t figure out where the end of the arc is supposed to be. The ends of segments in that arc are not necessarily at radius 1/4 from the desired center! Here is an example using the simple Arc tool after setting the number of sides to 8. Note that after clicking the center at the guide offset 1/4 from the straight edge, I use a red inference to find the start point on that edge. Then I swing the arc until I see a magenta inference that the arc is ending on the other curve.