A cookie management issue was addressed with improved checks. This issue affected versions prior to iOS 11.4.1, macOS High Sierra 10.13.6, tvOS 11.4.1, watchOS 4.3.2, iTunes 12.8 for Windows, iCloud for Windows 7.6.
https://support.apple.com/kb/HT208938
https://support.apple.com/kb/HT208937
https://support.apple.com/kb/HT208936
https://support.apple.com/kb/HT208935