I experienced the same annoying issue... and after resetting network settings, it went better for an hour... and started again, draining battery fast. I disabled the "background apps + automatic updates of Appstore"... nothing.
Then I realized that I had been doing IOS updates OTA and I remembered that in the past, it was explained that OTA updates are like an "onion" OS... which means, layer above layer after each update, slower and sometimes with more bugs than "clean IOS".
--> I did a backup of my iPhone... i downloaded IOS 11.0.3 IPSW and typed "restore"... to do a FULL RESTORE.
After restart... just restore from backup... and your IOS is clean. It works and it's been a few days that I can finally enjoy IOS11 properly. Hope this helps you. Remember that OTA updates are quite convenient, but for a major release update like from 10 to 11... a full restore is sometimes better and needed.