Same problem here
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Following exactly these instructions worked for me:
1) Unpair your phone from xcode
Launch xcode with your phone not plugged in
Plug your phone in
Under devices in xcode, unpair your phone
2) stop xcode
3) run these
rm -rf ~/Library/Developer/Xcode/iOS\ DeviceSupport
rm -rf ~/Library/Developer/Xcode/iOS\ Device\ Logs
rm -rf ~/Library/Developer/Xcode/DerivedData
4) start xcode
5) plug phone in