I came across problem with setup NFC reader on Xamarin IOS. Example of configurationn is here: https://docs.microsoft.com/en-us/xamarin/ios/platform/introduction-to-ios11/corenfc
After launching application the NFCNdefReaderSession.ReadingAvailable is always false and in device logs:
[NFCNDEFReaderSession beginSession]:255 error:Error Domain=NSCocoaErrorDomain Code=4099 "The connection to service named com.apple.nfcd.service.corenfc was invalidated from this process." UserInfo={NSDebugDescription=The connection to service named com.apple.nfcd.service.corenfc was invalidated from this process.}