Kurt,

About the unfilled loop: 3 out of 4 corners are coplanar, obvious (3 form a triangle and are always coplanar) One solution: the bottom corner near the green axis needs to be moved in the red AND green direction to fix things, to position it perfectly below the other endpoint of the vertical black line => result=blue.
But there is more going on here. These examples give the most problems because you do have the topline that shows as being on axis but it is NOT!! It is within tolerance, so to speak. The vertical black one is without tolerance hence shows black as it should.

To resume: the short vertical black has an angle with blue that is without tolerance while the longer top red edge has an angle within tolerance with red.

How to check: change your settings as follows:
Window > Model Info > Units > change Format: Fractional to Decimal with high precision.
Open your nested component to reach the bottom level, the edges and endpoints in question (i.e. ultimate edit mode).
Use the ‘Text’ tool to label the 4 endpoints. You will see following coordinates:

A= 13,559926", 2,049547", 12,394535" C= 10,567197", 2,049763", 12,394535"
B= 13,559926", 2,049547", 11,842216" D= 10,569578", 2,048282", 11,828312"

Here you can see that A and C don’t share the same green value hence aren’t even
on red axis.

How to fix this side is easy but how much that influences the rest of the geometry depends strongly on how accurate the rest is.
Redrawing the arc you should do only after fixing the position of the 4 vertices
(here: moving C AND D)

Hope this helps,
Wo3Dan

p.s. Why is correction important. When not, you will constantly get conficting situations for the inferencing engine 'gets confused' about inferencing with almost on axis endpoints and the corresponding axis itself