LTC2662 returns no fault registers

Dear Ladies and Gentlemen,

what could be the reason for a LTC2662-12 to clock out the correct echo readback (command, address and data word), but not the fault register bits on SDO while not processing commands?

My initialisation sequence, which worked in other projects implementing the LTC2662-12, looks like this:

Write Code to All/ Update All (command 0xA)

Write Span to All (command 0xE)

I swapped the chip twice, so  a non functional chip is ruled out in my opinion.

Supply voltages are in range.

Kind regards

Gunnar