The newer Hubs are no better - have you tried this...
If you haven't done this already - try it first - it helps sort some Hub3/4/5 wifi issues for some devices.
Go into the Hub’s settings. Type in http://192.168.0.1
into your web browser’s url box and login with settings password on the Hub's base sticker (or your own if you changed it). Then in Advanced>wireless signal >smart wifi - tick the disable “channel optimisation” box or “Smart Wifi” box and save settings. May be different pathways and wording on the 3 Hub types
Then, go to advanced>wireless signal>security, rename the 2.4 & 5 GHz network ssid's. Just type over to change 'em to whatever you like and something that will differentiate them (e.g - Billybob2 & Billybob5) Try to avoid spaces and periods in the SSID names as they can cause issues with certain devices. Use the same password for simplicity, Then, apply settings and restart the Hub. Your 2 wifi networks will now be clearly separated - and you can then select the network you want to connect to individually from the "available networks" list on each device.
Note all your wifi devices will need re-connecting to the new SSID's and passwords.
All things being equal, 5 GHz is always better/faster and subject to less congestion/interference (and is better for iDevice speeds than the 2.4 one - although the 2.4 one has the better "range" and will be needed when the 5 GHz drops out of range and some older/cheaper/dumber devices can only use this one.
You should also use a wifi analyser App (or Airport Utility on iOS) to check which 2.4 channels are being heavily used around you and move yours to one of numbers 1,6,11 that is least so, but it wont help if there is other interference.
See if these changes help - you will lose any “seamless roaming” benefits but it may not matter and you can always change the settings back by doing a " pinhole factory reset " if you prefer the way it was - or it doesn’t help.
I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.