I’ve been restoring all of my devices and noticed that iCloud Keychain was out of sync between my devices, through some testing I came across what looks to have kicked it back in sync.
- Check your iOS devices and turn off iCloud Keychain on all of them apart from the one where the Keychain is correct (see Settings --> Passwords & Accounts --> Website & App Passwords), I'd go with the device with the higher number
- Wait for around 20 minutes (vague I know but this seems to depend on how quick Apple's servers are working)
- Turn iCloud Keychain back on one device at a time
You want to be looking at the count within Settings -> Passwords & Accounts –> Website & App Passwords. The number should be in sync across all of your devices.