Firstly, please update the firmware manually by downloading it from here and uploading it via WebUI.
After you have completed the firmware update, please check if the device is working properly with a SIM card. If any configuration changes are needed, try making them via the WebUI first to ensure everything is functioning correctly. If further changes are necessary, you can use UCI.
If any issues arise, please provide a troubleshoot file. Since you lose access to the device and need to restart it to regain access, you will need to save the logs in the flash memory. To save the logs in the flash memory, navigate to System -> Administration -> Troubleshoot and change logging settings to save logs in flash memory. Don't forget to save and apply the changes. Afterwards, insert the SIM card and wait for 3-5 minutes to allow the router to establish a mobile connection. If you still cannot connect, restart the router to regain access, log in to the router, and download the troubleshoot file. Once the file has been downloaded, you can change the settings back to save the logs in RAM memory. Please attach the troubleshoot file by editing your question. The attached files are only visible to Teltonika moderators.