LTM4607 burns out


We have designed a power circuit for our application. For 24V/0.5A we've used LTM4607 regulator with 9V to 30V input. But we had some problems:
When input voltage is 9V - everything is OK. 12V, 24V, 27V - same. But if we start raising voltage to 30V - LTM4607 burns out. It seems like M1 or M2 transistors is broken. We have lost 3 LTM4607 by now.

About our implementation:
FCB pin is left unconnected, so the regulator should work in "Skip-Cycle Mode". SS pin pulldown by 0.1uF capacitor. Output current does not exceed 0.5A. A inductor - XAL7070-332ME. VFB pin pulldown by 3.4kOhm resistor. PLLFLTR pin voltage is 2.4V. Rsence is 10 mOhms.

What could be a problem here? Why do we lose the regulator in these conditions?

Also we use another two LTM4607 regulators to make 5V and 6V from same 9V to 30V input. And this regulators work fine.

Thank for help,

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