[engolling]

So I think this it not directly related with the software used but with the driver initializing the com port in Windows.

The driver, or the way the software uses the driver to open the COM port: for sure that CumulusMX and Cumulus1 are doing it differently, because the former always causes the freeze while the last not.
I don't remember for what purpose, but I have a very vague memory that some years ago I had to look on WeeWx serial driver code, to change from hardware handskake to Xon/ Xoff.

What I wanted to say is I think the issue is caused by the driver on a USB3 port - it also brings my WD unit to freeze on reboot.
CumulusMX is only the trigger doing some action to "highlight" the problem.