Hi Dazzapfc,
Thanks for taking the time to contact us via the Community. It's lovely having you on board with us in the Forums. ⭐
We're sorry to hear you're having an issue with some of your devices not finding the network even when on a split band.
This can sometimes happen if the devices are incompatible with WiFi 6. The teams will be able to change the Hub back to a 4 for you or as suggested by Client62, you can opt to use the Hub 5 in Modem mode and connect your own third party router. If you're prefer the Hub 4, give the team a call on 150 / 0345 454 1111.
Keep us posted on how you get on.
Thanks,