Hi Michael,
I've ordered an EVM for this product to replicate the issue you're having. In the meantime, for debugging purposes, can you try connecting /CS to a digital output on your MSP430 instead of GND? Most SPI interfaces need /CS to be able to toggle in order to reliably start and end SPI transactions.
I also noticed that you're programming reg 0x6 to 0 which would configure all GPIOs as inputs. Reg 0x6 should be set to 0xF to program GPIOs as outputs.
Please make sure that VOH and VOL are set correctly on the uC and that there isn't excessive ringing on the part's SPI inputs (esp SCLK) which can cause the part to reset. It would be a good idea to add 50 to 100 ohm series resistors to the SPI lines to limit the slew rate of the input signals and alleviate any ringing problems. You can also try decreasing SCLK frequency for limiting its slew rate.
Once you've written the correct value to reg 0x06, I'd recommend reading back the contents multiple times to ensure data integrity before writing to reg 0x05 to toggle the outputs. Please let me know if you observe a change in your results.
Best Regards,
Harsha