UCC2897A: The clamp P-MOS waveform isn't right when do the tests of UCC2897A

Hi team，

My customer is using the UCC2897A now. When they do low temperature test -30°C，the waveform is weird. The yellow is Vgs of P-MOS,green is the Vds of  P-Mos. The blue is VDD, the red is the Vss.

The weird waveform shows. When VCC trigger UVLO, the P-mos should be no drive signal. The drive voltage is 4~5V.

could you please help check the reason of the problem?

thanks.