Thank you for posting about your experience with the ZTE MF275R Rocket Hub.
Getting reliable speeds is extremely important, especially when it comes to your household internet connection. We want to help you resolve the ongoing slow speeds issues you've been experiencing.
Are you running your speed tests using a wired connection (Ethernet cable) from the hub to the device you're running tests on, or are we looking at Wi-Fi speeds? Are there other devices connected to the Wi-Fi network while you are running them?
Some MF275R users reported getting higher speeds when turning LTE off.
This might be a long shot but could you try this and let us know if it helps in your case?
I can appreciate your position; slow speeds can be bothersome. It's good to know that you are well versed with configuring your hub.
We will appreciate if you can list all the troubleshooting done so that the Community can share their expertise to find a solution.
It seems something has changed in the past six months resulting in slow speeds even though you have all green lights on the hub. How far is the nearest tower from your location?
I'm not sure if you tried testing speeds from other locations. If you are getting good speeds from other locations or when you are close to a tower then you can consider an external antenna. Please check "Rocket HUB external antenna" thread for extensive discussion.