I’m facing the same: more crashes of the modem. I produced months before the following script:
#!/bin/sh
# from https://source.puri.sm/Librem5/linux-next/-/issues/303
#
# Clayton Craft @craftyguy
# Contributor
# 
# I've been using the following script to "recover" the modem when it
# disappears, it seems to work every time for me:
set -x
sudo rmmod xhci_plat_hcd xhci_hcd
echo 0 | sudo tee /sys/class/leds/wwan_en/brightness
sleep 2
sudo modprobe xhci_plat_hcd
sleep 5
echo 1 | sudo tee /sys/class/leds/wwan_en/brightness
# added by guru@unixarea.de
#
sleep 5
sudo systemctl restart ModemManager