iCloud immediately logs me out

Starting this morning, when I use Safari (El Capitan 10.11.5), after I log in to iCloud, I see all my icons. But if I wait just a minute, it logs me out and I have to enter my AppleID/password again. Whether I open a spreadsheet in Numbers, or check my account details, as soon as I get going, I go back to the main page, and then to the login page.

Starting this morning mind you!

I had no problems between my iPhone 6P (iOS 9.3.2) and my MacbookPro syncing Numbers, contacts, etc. But as soon as I turned on iCloud on my Macbook, all my spreadsheets disappeared from the Cloud in Finder, and the ones in iCloud could not be opened, and had to be duplicated.

what is going on here?