SIM800C going Off after i detach the USB

I build a device that using ESP32 and SIM800C that generally hit API for a certain period times. This devices powered by AC but also can be powered via USB. When I upload the code it running well and can hit the api. but when i release the usb from the board after a certain times 2-3 hours it not hit the API anymore. My Guess is there are unstable voltage that make the SIM is Overvoltage or undervoltage but i want to hear your opinion and how to overcome this problem. Also is there any solution how to log any issues on sim to SPIFFS. Thank you

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