iPad no longer connecting to iTunes

Since updating to iTunes 12.7, MacOS Sierra and iOS 11 I now constantly get the following message in iTunes:

" iTunes could not connect to the iPad “Dave's iPad mini” because it is locked with a passcode. You must enter your passcode on the iPad before it can be used with iTunes"

It's a retina iPad mini. My iPhone 7 Plus has no such issue. and they are both set to sync over WiFi, although I have tried connecting with a USB which worked fine.