ADS1220 LSByte always 0x00

I'm using the ADS1220 with an ESP8266 in the Arduino environment. I can write all of the configuration registers and read them back. I can kick off a continuous mode conversion and read back the results, but the last byte is always 0x00. I am not monitoring the /DRDY pin and I have DRDYM = 0. Therefore, I issue an 0x10 RDATA command and immediately follow it with a 3 byte read. /CS is low the entire time. No matter what, the lower byte is always 0. The upper bytes change appropriately with changes in the input, and the output results are close, I'm just missing that lower byte. Any idea what could be causing this? What additional information could help troubleshoot? I've been working on this for a while now and I've made a mess of the code trying to fix it. Haha.