AD9524 PLL2 don't lock at low temperature

Hi All !!!

I'm using AD9524 PLL2 to generate 5 clocks 64MHz from 32MHz cristal oscillator. All work fine at my table. But I have problem in heat chamber at low temperature.

When AD9524 is locked at -10 degrees, for example and cool up to -40 degrees all work fine, but when AD9524 is power on at -40 degrees PLL2 don't lock at all %(. And need to warm up AD9524 to -20 degrees to bring it work again.

PLL2 settings is

Loop BW 251kHz, Phase Margin 65.2deg, Zero Loc 63.7kHz, PoleLock 1.38MHz, Last Pole Lock 67MHz.

Cristal oscilator i using is Rakon TXO725E with specified working temperature is -40...+85. AD9524 specified working temperature is -40...+85 too, but it don't worked. What i do wrong ?

Thanks a lot!!!