iCloud mail folders disappeared

I have all my mail folders synchronised from the cloud, iCloud. I use an iPhone, a MacBook Air and an iMac, which all use Apple Mail and all get the mail from iCloud.

As from yesterday afternoon, i am missing almost all of my mail folders in Apple Mail. Also, my three Inbox folders only contain mail as from yesterday afternoon. Some other mail folders contain all the mails that where there until yesterday afternoon. Also, when logging into iCloud.com I see the same...

Does anyone have any idea how this can happen and how to resolve?

Thanks in advance!! Grtzz Renzo.