If I apply 0V → 3.3V to SHDN and then supply IN voltage, it may not start.
Is there a limit to the sequence?
I look forward to your reply
there is no sequence mentioned in the datasheet. But keep in mind that the LTC4359 is powered via the IN pin, hence any voltage applied to SHDN before VIN is available has no effect on the part.
Have you tried Vin first first, then shdn? What happens then?
Your complete schematic and setup would be helpful/necessary for detailed support.