BC20NA doesn't restart

Hello,i have some problems with my BC20 module using OPEN CPU.
The following are some feastures of my item:
1.My power supply is the battery with maxium current 400mA.
2.Its a low power item with PSM mode.
3.The SW version is BC20NAR01A09.
The problem is:
Firtstly,does the BC20 resart after the supply drop and resume a normal phenomenon? If so,why my module’s power on reason is system reset(power on reason equals to 2),and not restart automatically?(i guess the power low cause module drop,but why the power on reason is 2.)
Secondly,why the module power on reason is 0 when i start the power supply?And ,only after i give the cammand “AT+QPOWD=0” to power off the module ,the power on reason could be 3(the power shut down).
The last one,how much voltage dorp level could be normal if i use the battery supply?

  1. The module considers the reset as the system reset, and does not distinguish the cause of the restart.

  2. The first time the power is booted up is the first time the power is turned on.

  3. In the data transmission work of the module, the power supply drop must not be lower than the minimum working voltage of the module 2.1V, otherwise the module will be abnormal.

I hope my answer is helpful to you.