Try to create a plugin for modemmanager. get "Network device is not present"

Hi. i try to create a plugon for the FM350gl wwan card in usb mode.
In USB Mode tty an rndis protocol is in use.
in the gui i can select the card and create the ModemManager interface
the output from mmcli is:

root@OpenWrt:/# mmcli -m 1
  --------------------------------
  General  |                 path: /org/freedesktop/ModemManager1/Modem/1
           |            device id: XXXXXXXXXXXXXXXXXXXXXXXXX
  --------------------------------
  Hardware |         manufacturer: Fibocom Wireless Inc.
           |                model: FM350-GL
           |    firmware revision: 81600.0000.00.29.21.24
           |            supported: gsm-umts, lte
           |              current: gsm-umts, lte
  --------------------------------
  System   |               device: /sys/devices/platform/soc/11200000.usb/usb1/1-1/1-1.4/1-1.4.4/1-1.4.4.3
           |              drivers: rndis_host, option1
           |               plugin: fm350gl
           |         primary port: ttyUSB4
           |                ports: eth3 (net), ttyUSB4 (at)
  --------------------------------
  Numbers  |                  own: XXXXXXXXXXX
  --------------------------------
  Status   |       unlock retries: sim-pin (3), sim-puk (10), sim-pin2 (3), sim-puk2 (10)
           |                state: disabled
           |          power state: on
  --------------------------------
  Modes    |            supported: allowed: 3g; preferred: none
           |                       allowed: 4g; preferred: none
           |                       allowed: 3g, 4g; preferred: none
           |                       allowed: 5g; preferred: none
           |                       allowed: 3g, 5g; preferred: none
           |                       allowed: 4g, 5g; preferred: none
           |                       allowed: 3g, 4g, 5g; preferred: none
           |              current: allowed: 3g, 4g, 5g; preferred: none
  --------------------------------
  IP       |            supported: ipv4, ipv6, ipv4v6
  --------------------------------
  3GPP EPS | ue mode of operation: csps-2
  --------------------------------
  SIM      |     primary sim path: /org/freedesktop/ModemManager1/SIM/1

the Ports are detected : ports: eth3 (net), ttyUSB4 (at)
but in the luci gui i get the messag "Network device is not present"
and openwrt not start connecting.
if i start manaly with mmcli -m 1 --simple-connect=... ModemManager starts connecting

why modemmanager not detect the network device?

with a other card the logs show a hotplug interface ist set. bit with the FM450gl card the hotplug interface is not set? how can i force to set it?

i have found a line in the log from netifd
"Segmentation faul (core dumped)"
so how can i find out on what call its crash?