Hello,
I would like to ask if firmware update was performed with Keep settings option set to on? If that is the case, could you try resetting the device to factory defaults and checking if that changes anything.
The next option would be to enable traffic monitoring on mobile WAN interface. In the WebUI, navigate to System -> Administration -> Troubleshoot page. Under Troubleshoot section set Enable TCP dump option to on. Select wwan0 interface, Save and apply settings. Leave the device for some time to capture packets.
Afterwards, download TCP dump file from the same page. You can analyze it with Wireshark or attach it by editing your question for us to take a look at it.
Best regards,