The recommended troubleshooting steps in this circumstance (can connect once, but not again on OSX), are to first check if the FTDI driver is installed by following these steps:
Open Applications → Utilities → Terminal and run the following command:
kextstat | grep FTDI
You’ll see a line including either
com.apple.driver.AppleUSBFTDI (for the driver from Apple, which we recommend using) or
com.FTDI.driver.FTDIUSBSerialDriver (for the driver from FTDI, which we recommend against). It’s also possible that you’ll see them both. If both are present, then your computer will use the driver supplied by FTDI.
You can uninstall FTDI’s driver using the following command:
rm -r /Library/Extensions/FTDIUSBSerialDriver.kext
The FTDI driver is not recommended on recent versions of OSX.