The router is losing the connection to the modem. This is most likely due to a faulty LTE modem.
You can try flashing the device firmware to check if that could solve the issue, but there's a low chance of this working.
Since the warranty is still valid for the device. I would recommend turning it in for a warranty to the place of purchase with the cause of a faulty LTE modem, this is something we provide a warranty coverage to