Perhaps, you can search further online on how to restart a serial port on MAC OSX. If the software is causing the problem, possibly update to the latest version, reinstall the program, or reach out the manufacturer about this.
As for the 'not logging' interference, even though the device is paired up with the computer via bluetooth, it should still log data. The manual states that when you open up the Data Logger PC Utility software and starts to load data from the unit that is when it goes to 'Data Transfer' mode. In other words, the trackpoints are being loaded from the device and transferred to your computer. After you have obtained the data, you will need to restart the unit to be able to go back to the 'DataLogging' Mode.