If you haven't already don it, make sure you turn off "smart setup" on the Homehub.
See link how to do that.
Some devices have a problem with the Homehub dual band having the same SSid (name). You should try splitting them.
The Smarthub is not as good as the hype. If your HH3 is working ok you should stick with it.
If you split the SSids you will need to connect all your devices that can use the 5Ghz Said to it. Not all devices can use it so don't panic if they can not all see it when you scan for the new Said.
Some devices drop 5G connections (for example we had a Windows 10 laptop that did just this). We configured the laptop to connect on 2.4 only, and it has been rock solid ever since. I have heard of some mobile phones doing the same too.