This is not a NetworkManager problem. It is also reported by me in https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1950385 and it is probably kernel bug. The problem is described by ModemManager's developer in our discussion: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/463#note_1157289 as a broken USB communication. According to diagnosis from kernel 5.1x the qmi_wwan module resets modem firmware in endless loop: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/463#note_1157919 although it was worked flawlessly earlier in kernel 5.8.x
The workaround is to use udev script for a modem to switch it to the MBIM mode which works ok under ModemManager & NetworkManager. Reboot. Recreate connection profile for modem in Network Manager Mobile Broadband Settings for your GSM Network Provider to make it binded with new MBiM devid config. Tested on kernels 5.8, 5,11, 5.13. Place the attached udev script file in: /etc/udev/rules.d instead of any old one. It uses usb_modeswitch to do the "magic" correctly. ** Attachment removed: "Udev script for switching modem" https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1574582/+attachment/5541060/+files/99-hp-lt4120.rules ** Attachment added: "udev script for modem" https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1574582/+attachment/5541062/+files/99-hp-lt4120.rules -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1574582 Title: HP lt4120 Snapdragon X5 LTE USB modem not recognized by network- manager To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1574582/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
