iCloud Photo can't turn on after iCloud was singed out automatically.

[larryisthere]

I found iCloud was inexplicably signed out automatically when I noticed my e-mail accounts (include iCloud account and a 3rd party account) in Email.app was disappeared, and all my e-mails were gone. Then I went to System Preference Settings pane to check iCloud's status when I found that my iCloud was signed out without my operation. I tried to turn all items on and iCloud photo failed and gave me this contradictory stupid alert. My HDD format is APFS which matches its request, and the most important part is I didn't do anything to it. By now, my documents still can't be downloaded from iCloud ...

Weird, bug or anything else?