To clarify, I have been using Apple hardware/software since the Apple II+ was new.
I have been using iCloud to sync across all devices since that became available (years ago).
All was working well until just recently; maybe 2-3 months ago I noticed that my iPad Pro Safari was not sync'd with my iMac Pro Safari (also, my iPhone XS Safari was not sync'd to my iMac Pro Safari).
I turned on the iCloud Keychain feature on each of my devices when they were new out of the box and have not turned it off on any of them since. All devices are always running the latest OS; I install all updates within 24-48 hours of availability.
I have confirmed that iCloud Keychains is turned "on" and active on all devices; I have the iOS devices configured to sync over Wi-Fi; my Wi-Fi network uses the Apple Airport; the signal is strong -- I'm within 10 feet of the Airport router.
The only reasonable explanation is that iCloud Keychain was changed/modified/corrupted during either an iOS update on the iPhone or iPad, or during a Mac OS update on the iMac.
When I open the iMac Pro Safari app "preferences" and compare the password list to the iPad Pro password list, it is obvious that the two systems are not syncing.
I had the iMac and iPad connected by cable yesterday, performed several "sync" sessions, and the Safari passwords are not sync'd. The sync resolved a separate problem with the Podcast app content, but did not seem to affect the Safari passwords.
