I encountered the same issue as described in Topic 51817.
I resolved the issue using the following steps:
- Disconnect the external Wi-Fi that the MT3000 is connected to, and then turn off the router’s Wi-Fi.
- Connect to the router via the local area network.
- Perform the upgrade locally by re-uploading the v4.7.4 upgrade file.
I downloaded the upgrade file from here.
These steps were recommended to me by the support team.