We needed to switch off Known Folder Move and then switch it back on again.
By trial and error we discovered registry values that are set by KFM, and need to be deleted.
Is there a list of the purpose of these values somewhere?
HKCU\SOFTWARE\Microsoft\OneDrive\
KfmFolderNotSyncingMessageHandled
HKEY_CURRENT_USER\SOFTWARE\Microsoft\OneDrive\Accounts\Business1
KfmFoldersProtectedNow
KfmAcmAdminMessageState
KfmHasForceShownWindow
KfmIsDoneSilentOptIn
KfmSilentAttemptedFolders
