AD9144 unexpected power-down

At the final write in the flow (write 0x01 to reg 0x300), I find that I sometimes need to write to it twice to actually read 0x01 from it.

Regs 0x470-0x473 are all reading 0xFF, which is good!

But on the output of the DAC we see inconsistencies. We see one of 4 outcomes:

1. All 4 DACs are operating properly (outputs are as expected).

2. Only DACs 0 & 1 are working properly. DACs 2 & 3 seem to be powered-down.

3. Only DACs 2 & 3 are working properly. DACs 0 & 1 seem to be powered-down.

4. None of the DACs work properly.

We have checked that the TXEn pins are both high.

Would very much appreciate any insight you might have!