Possibly you not correct read values from file?
NanoVNA
50000 -1.00041697950416 0.007368446112387565
ZNC3
5.000000000000000E4 -1.000193611347694 6.168578964723261E-3
Values ~equal, but ZNC3 use exp format for store

Or get next random string
NanoVNA
29520500 -0.009519632466691198 0.38243573049738105
ZNC3
2.952462809917355E7 -7.411973193649163E-2 3.916175087556830E-1
Also ~equal

from nanovna.

Thanks for your hint.
This is not the issue.
The issue is what is coming after the frequency, the content of the S11 value.
There it goes wrong.
Although the headers of both the ZNC and the nanoVNA specify

Hz S RI R 50

this seems for the nano VNA

• or not to be true but is possibly is another format or:

• the format is true but the numeric values are errrornous.
  I want that to be cleared so i can proceed my calculations.

from nanovna.