Hello @Ad13 ,
Since the part able to boot for some short time, that's mean there is a fault triggered.
So could you please share your schematic for EM2130_0.9V rail and also please provide a waveform for Vout during the fault.
Also the rail could shutdown if you are using a sequencer to control the on/off sequence and that controller bring the rail off.
So please also probe CTRL signal too incase that signal pull down after the power on.
Probably you are not able to communicate with the regulator through PMBUS if the bus is busy or the 5VCC is off.
Thanks,
Mostafa