Same here on iPhone 5, EE. Weird thing is last night after updating OTA to beta 2 I had 4G. This morning I had 3G showing and toggle in settings was enable 3G. Rebooted and this changed to enable 4G but it wont connect to a 4G network.
Very annoying!
There's a bug in the beta for sure..
I have no additional apps on the ipad except my own app for testing. All the setting are as default. I downgraded back to 7.1.1 and 4G works fine.
Back to 8 beta 2 and no 4G again. Curiously, iPad says I have no connection to the cellular network while showing full bars and 3G.
Works fine with 7.1.1