A cross-origin issue existed with "iframe" elements. This was addressed with improved tracking of security origins. This issue affected versions prior to iOS 12, watchOS 5, Safari 12, iTunes 12.9 for Windows, iCloud for Windows 7.7.
https://support.apple.com/kb/HT209141
https://support.apple.com/kb/HT209140
https://support.apple.com/kb/HT209109