The 4G routers are configured for auto network selection. There is sometimes a requirement for a minor settings change to be made if the internet does not work when changing network provider.
Sometimes the APN (Access Point Name) is required to be updated.
This can either be updated via using the Huawei Hi Link App or by accessing the Router settings page.
To update via the App. Download the Huawei Hi Link app from the app store on your mobile or tablet.