One of the problems we experience when using FTDI chips on Windows is that they often get remapped to a different COM port every time the device is removed and plugged back in again.
Dangerous Prototype has provided a workaround based on a KB from FTDI
“Ever notice that each new FT232 inserted into each USB port is assigned a unique COM port number under Windows? When we’re developing hardware with lots of prototypes flying around Windows quickly hits COM 100. Each FT232 has a unique serial number and the driver creates a new COM port for each by default.”
Read more on Dangerous Prototype’s page