No iCloud keychain sync anymore with a specific AppleID

The iCloud keychain sync between my devices doesn't work anymore with my current AppleID. I doesn't matter, which way.

All settings are correct (yes, really, don't ask ;-)), disabling/enabling/deleting/reinstalling have no impact. But, if I use another AppleID, it works fine!

For me, it seems to be a bug. Anyone else with the same problem?