2.4Ghz / Optimisation

Hello. I have been with VM for around a year and have the Fibre M250 package. I always struggle for WiFi in other rooms (I only live in a small flat).
I have my WiFi split 2.4Ghz and 5Ghz because I have smart home devices that only work with 2.4Ghz.

In the living room where my Hub3 is located, I connect to 5Ghz and get 250Mbps. However, in any other room I have to connect to the 2.4Ghz and then I can less than 15Mbps.

Today, I decided to have a play with settings in the app. I joined the 5Ghz and 2.4Ghz bands together as the app suggested for optimisation. To my shock, I can over 150Mbps in every single room, so I’m very happy.

However, none of my smart home stuff now works because the 2.3Ghz band is no longer available to connect the devices to.

Is there a way around this? I don’t partially want to split the bands again as the download speed is very good now.

Thanks.