LTC6813 responding with 0xFF for everything

I'm using the LTC6813 on a custom built PCB, and have the reference Linduino software that I got from here running on an Arduino Uno.

The VREG bus is at 5.25V and then turns off after 2s if no command is received(as expected), however, the VREF1 and VREF2 pins are at 0V.

When the evaluation software requests information from the device of any sort, the SDO is held high (0xFF) during the data part of the transmission, but a PEC of 0x66, 0x4C is transmitted as well. 

When I send the command "1" to the Linduino software (Write and Read Configuration: 1), I get this as the output - 

Written Configuration:
CFGA IC 1, 0xE4, 0x0D, 0x28, 0xA0, 0x01, 0x00, Calculated PEC: 0xAD, 0x6A
CFGB IC 1, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, Calculated PEC: 0xC2, 0x12

Received Configuration
CFGA IC 1, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, Received PEC: 0x66, 0x4C
CFGB IC 1, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, Received PEC: 0x66, 0x4C

Reading cell voltages in a loop (command 11) gives me -

Cells, 6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,6.5535,

I am unsure what is going on since obviously the chip is responding to commands with messages that have a valid PEC value. 

Thanks in advance, I'm happy to provide any more information that you'd like, including schematics of the board to find any hardware issues, if there are any.