BG77 raspberry Pi 4 64 bit driver

I have connected BG77 using usb to PI. Also I am able to create PPP connection but when RPI reboots, modem is not detected. it resolves by reconnecting usb cable of Modem.

As you mentioned, once the BG77 restart, the RPI could not recognize the modem. It is caused by hardware issue. Please check the power and the USB cable.Maybe the USB cable is too long.