If I read your post correctly,
"nanoVNA-H4 hardware build 4.3 using the NanoVNA-H.v1.2.40.bin "
Your problem is you used the WRONG firmware!!!
You can not use "H" firmware on a "H4"!!!!!
And expect it to work correctly.
They are two different NVA's
First, download and install the Firmware for the NanoVNA H4, then try it.
Clyde KC7BJE
Clyde Lambert