Error base network connection interrupted

[Denis Ronchese <teoman_93 yahoo it>]

Hi!

I'm currently working with a SimCom SIM7000E-based Raspberry hat, using ModemManager and NetworkManager to 
handle the GSM connection (and the GPS location data too). 
Raspberry OS version is 10 (buster), ModemManager version is 1.10.0, NetworkManager version is 1.14.6, qmicli 
version is 1.22.0.

So, my problem is that I'm facing an error that I couldn't manage to solve: when I try to activate an already 
created connection through "nmcli con up", Network Manager couldn't do it, raising this error message "the 
base network connection was interrupted". In the same exact time, ModemManager seems to lose the USB 
connection to the modem, and regain it after the usual 15-20 seconds.

This error appears at random times and, in the attempt to work around this, I already tried the HW reboot of 
the modem (through its reset pin) and the reboot of the system, as well as the restart of the nmcli and mmcli 
processes, without success.
After some time, the connection seems to activate correctly again.

Any ideas on why this happens?