I’m not sure why the driver for serial2 doesn’t load with your setup as it seems you do everything correctly. However, it seems, that disabling UART B helps. In order to solve the issue, you could use the workaround as proposed by Samuel initially. Just create a small tool which runs at the beginning (or add some code to your application before opening the serial ports) which adds a pull-up resistor to CTS. Note, when adding a pull-up to CTS of UART B, this will automatically also add a pull-up on all other UART B signals (RXD, TXD, RTS). This cannot be avoided on the T20. You can use the GPIO Library in order to set pull-resistors for signals.
Another approach would be to add a real external pull-up resistor, or try to set CTS as GPIO output 1 also using the GPIO Lib. Setting GPIOs to output can be done w/o affecting the other UART B GPIOs.
I hope one of these workarounds will help.