(Same with a HP un2400 Gobi1000 module) Sometimes we see a USB disconnect message in our kern.log. As a temporary solution we autoreboot our pcengines apu1d4 system.
usb 1-1: USB disconnect, device number 2qmi_wwan 1-1:1.0 wwan0: unregister 'qmi_wwan' usb-0000:00:12.2-1, WWAN/QMI device
option1 ttyUSB1: usb_wwan_indat_callback: resubmit read urb failed. (-19)