Raspberry Pi 3G-4G/LTE Base Shield V2 Comport /dev/ttyUSB1-3 Disappear

Hi I am using a RaspberryPi 4b and a 3G/4G & LTE Base Shield. The shield works perfectly however, I seem to get into a situation where if I exit the process the serial ports disappear i.e. /dev/ttyUSB1-3 are no longer available. If I reboot the Raspberry Pi they don’t return and I have to power cycle the Raspberry Pi to get them back.
This happens on all the Shields (10) I have.

Thank you


Could you please share the status of your GPIO pins during all stages?

NOTE: Check the GPIO26 which should be always LOW.