Sierra WWAN LTE Modem EM7305 does not work after Suspend/Resume

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I need some help with getting my WWAN modem to work after Supsend/Resume.

This is a Fujitsu U904 with a Sierra EM7305 LTE WWAN modem running Fedora 26 with Gnome. It works perfectly when the laptop is freshly booted. However, it consistently stops working after a Suspend/Resume cycle. It is then either listed as "unavailable" in the top right menu or it is not listed at all (no Wireless Broadband entry).

I've also tried this with Live versions of Suse Tumbleweed and Ubuntu 16.04 and 17.10. It is exactly the same with these.

Below is the output from lsusb, usb-devices and debug output of ModemManager. There is an error at the very end of the ModemManager debug output which I suspect points in the right direction:

ModemManager[18077]: <warn>  [1506494462.458943] [mm-base-manager.c:167] device_support_check_ready(): Couldn't create modem for device at '/sys/devices/pci0000:00/0000:00:14.0/usb1/1-6': Failed to find primary AT port

I'd be grateful for any clues about what to do about this.

# lsusb

Bus 001 Device 008: ID 1199:9041 Sierra Wireless, Inc.

# usb-devices

T:  Bus=01 Lev=01 Prnt=01 Port=05 Cnt=04 Dev#=  8 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  2
P:  Vendor=1199 ProdID=9041 Rev=00.06
S:  Manufacturer=Sierra Wireless, Incorporated
S:  Product=EM7305
C:  #Ifs= 2 Cfg#= 2 Atr=e0 MxPwr=500mA
I:  If#=12 Alt= 0 #EPs= 1 Cls=02(commc) Sub=0e Prot=00 Driver=cdc_mbim
I:  If#=13 Alt= 1 #EPs= 2 Cls=0a(data ) Sub=00 Prot=02 Driver=cdc_mbim

# systemctl stop ModemManager 
# /usr/sbin/ModemManager --debug

ModemManager[18077]: <info>  [1506494430.795234] [main.c:158] main(): ModemManager (version 1.6.4-2.fc26) starting in system bus...
ModemManager[18077]: <debug> [1506494430.796125] [mm-sleep-monitor.c:245] mm_sleep_monitor_get(): create MMSleepMonitor singleton (0x55fb29873860)
ModemManager[18077]: <debug> [1506494430.798615] [main.c:83] bus_acquired_cb(): Bus acquired, creating manager...
ModemManager[18077]: <debug> [1506494430.799152] [mm-plugin-manager.c:1559] load_plugins(): [plugin manager] looking for plugins in '/usr/lib64/ModemManager'
ModemManager[18077]: <debug> [1506494430.799516] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Motorola'
ModemManager[18077]: <debug> [1506494430.799784] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Samsung'
ModemManager[18077]: <debug> [1506494430.799940] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'X22X'
ModemManager[18077]: <debug> [1506494430.800129] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Altair LTE'
ModemManager[18077]: <debug> [1506494430.800375] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Option High-Speed'
ModemManager[18077]: <debug> [1506494430.800575] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Nokia (Icera)'
ModemManager[18077]: <debug> [1506494430.800739] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Telit'
ModemManager[18077]: <debug> [1506494430.800836] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'AnyDATA'
ModemManager[18077]: <debug> [1506494430.800977] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'Thuraya'
ModemManager[18077]: <debug> [1506494430.801168] [mm-plugin-manager.c:1584] load_plugins(): [plugin manager] loaded plugin 'ZTE'
ModemManager[18077]: <debug> [1506494430.801373] [mm-plugin-manager.c:1584] load_plugins(): [plugin ...