Focus curve error?

Does the focus curve start well and then in the second half does any idea fail to solve it?
video focus curve

Is this the usual shape of the focus curve with your equipment, particularly with good weather?
Specifically for this curve after collecting all requested data points, the quality is 87%, which is less than the default 90% required for the quadratic fit routine to accept it. So it does a repeat looking for a better curve. If this is common you may need to set your quality threshold to a lower number, perhaps 80 or 85%.

where it can be modified, the funny thing is that it makes a nail

What does “makes a nail” mean?

Here is where I have set mine:
FocusQualityThreshold

ok thanks, what I was trying to say last month didn’t fail

At some point we will add this to the UI, but I’d like to keep it out of the main AF settings area into an “advanced” area that does not yet exist.