I attempted to use SV6301A which I have, It does shows up and after I connect showing correct firmware number.
I am speculating the issue in your code is related to 1001 points vs 501 points which your current VNA's support.
I can try to force it to 501 and see if that shows up anything. With my default 1001, there is not error or change on the screen except the firmware version.
Do you have builtin logging with various levels of verbosity so in such cases users can attach here?
Here is a screenshot for the latest version downloaded today Version 1.2 (6)
The three previous VNA in the list do produce the same output in attached screenshot. The new VNA model when select is prompting me about calibration stating the master calibration is missing. But my SV6301A has been calibrated.
As I mentioned, the firmware version is reported correctly. So something is working. Please note, no antenna is connected, since I just wanted to get a quick screenshots.
I am running latest upcoming Tahoe 26 beta since I am testing my apps. Final version is expected to be released next week on Sep 8/9.
I will run it again in couple of hours and will send you a screenshot.