Bob,
If you ever decide to upgrade your firmware you may run into something similar. My second NanoVNA arrived with only the 2 trace firmware installed. When I tried to upgrade to the 4 trace firmware it wouldn't take correctly. The solution was to first install CLEAR_MEMORY_DFU and then install the 4 trace DFU. Its not always necessary, but I now use it as a matter of course to prevent artifacts left over from the previous install from causing hard to track down problems.
Herb
