I am on MacOS 10.15.3. I don't think the serial problem is with your software. Is shows up as a serial port and I can access it with many other programs. The problem is with the way nanoVNA-saver software handles errors. No matter the data you send, nanoV shouldn't crash. If I have nothing connected to the AVNA input terminals, nanoV will crash after a bunch of (probably 101):
NanoVNASaver.SweepWorker - WARNING - Got a non-float data value: -34.626995 -46.589237 (-34.626995)
NanoVNASaver.Hardware - ERROR - Exception while reading data 1: Attempting to use a port that is not open
I forgot to mention that having the 50 ohm termination on during CALSAVE 1 did seem to make less noise as you mentioned.
Interesting you knew Phil Smith. I don't think I'm that old at 64, but my first year of engineering in 1973 was the last year that slide rulers were required at University of Wisconsin - Madison engineering. I still have it.
The PVC pipe inductor sounds interesting.