Hi,
I've checked you're data and I saw that your raw data is starting at 8999.9999999999982 Hz and your definitions for the cal standards are starting at 9000.000000000000 Hz.
You can check that yourself by setting the numeric format to e16 in Table of the Data Explorer.
In the interpolation routine of VNA Tools (UncLib) I check for extrapolation using the following line of code
if (xx < x[0] || x[n1 - 1] < xx) return nan;
This returns nan for your problem at 9 kHz.
I've improved this morning this check by taking into account the epsilon of a double number. So the code looks now like that:
if (!(DoubleHelper.IsLessOrApproximatelyEqual(x[0], xx) && DoubleHelper.IsLessOrApproximatelyEqual(xx, x[n1 -1]))) return nan;
This will fix your issue, but it's not getting released with the next version 2.4.2 of VNA Tools. It will be part of VNA Tools V2.4.3 (around April 2021).
Workarounds for the moment.
Change the start frequency on the VNA to 9000.0001 Hz
Or try to use a segment sweep instead of linear sweep.
Or if the above two workarounds fail I can provide you a script which replaced the first frequency point of your raw data by 9.000 kHz.
Hope this helps.
Regards
Michael