Summary
When you try to reopen recently opened cloud documents from the Your files tab on the homescreen, you get the error Can't open file. The account you signed in with doesn't have access to this file.
As a workaround, reopen recently opened cloud documents from the Recent section in the Home tab on the homescreen. To fix the error that you get in the Your files tab, reinstall the CoreSync process by running the Creative Cloud Cleaner tool: