Having the same problem, but its with pages not working via icloud.com using a web browser. Unable to open a previously stored document, or even open up create a new document.
I contacted icloud support and they had to send me to second level. Second level couldn't figure it out, and thought it was because I was using a pc - That can not be the problem, because It doesn't work on two different pc computers (different windows systems) And My business account is the one where I can't open or create documents via icloud.com - but I can from my ios device. But my personal icloud.com works just fine on either machine. Second level is sending the ticket up to engineering and may be 3 days before I hear an update.