very interesting that this modem only have QMI mode and has two cdc-wdm device.

Seems there is a problem because the modem shows registered and then unregistered for several times.

Can you upload to firmware v2.261 if the version is older? There maybe a problem in setting up qmi mode.

Then can you try cdc-wdm0 as well?

You can post the content of /etc/config/network because we didn’t have experience to deal with two cdc-wdm device and the UI may post wrong settings to the mifi.