Did you find any resolution on this? I also have an Epson SX425W and just had my HUB changed to 3.0. Cant connect and tried all the usual stuff. Driving me crazy. I am a real technophobe so banging my head against a wall here.
I would say that the root cause of not being able to connect a 2.4GHz printer to your Hub3's 2.4 network rests either in having "channel optimisation" activated - which just messes up 2.4 connections completely IMHO. And also because it has the same ssid as the 5GHz one - and this wont help a confused device to sort out how it should connect. So switch off channel optimisation & reboot the Hub. Switch the printer off for a few minutes then on again and clear all previous connections from its "menu" and then set it up as the instruction manual describes for a first time connection to a new wifi network. If that still doesnt work, rename the ssid's of the 2.4/5 networks and repeat and "force" it onto that now separate network. If that doesnt work use a wifi channel optimising App and probe which of the 3 "usable channels (1,6,11) is least congested in your location - and if your 2.4 network is not on that one - switch it to it.
-------------------- John --------------------
My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.