iCloud Keychain and Passwords disappeared

My iCloud keychain passwords are not working suddenly, in Safari on macOS. I am running Catalina 10.15.5 on a newer 2019 iMac. The problem: I went to enter one of my work websites in Safari and my password autofill isn’t popping up. So then I went into Safari preferences to check my saved passwords and the list is entirely blank. There should be hundreds of saved passwords in there. System preferences shows that Keychain access is allowed under iCloud settings. But the Keychain Access app is showing the iCloud Passwords keychain as being blank.

In an attempt to troubleshoot, I have tried turning off iCloud Keychain in System Preferences, by un-checking the Keychain selector under iCloud setting. I go through the authorization process by entering my account password for my appleID, but then the system preferences window just reverts to showing it as check-marked. I was hoping I could turn it off and then back on to restart the keychain sharing on this machine. But I guess it won’t let me even get that far in troubleshooting. I don’t want to reset the whole keychain in the Keychain Access app, because I am using this keychain on three other devices, and there is no problem on them. I don’t want to lose nine years of saved passwords and certificates.

Oddly, I still have the 2013 iMac which is the machine I recently migrated from. It is logged in to the same iCloud account, but it is not demonstrating this problem in Safari. The iCloud Keychain is still working properly on that one, running the same macOS install of 10.15.5. And Keychain Access shows my passwords keychain as fully populated.