Trying to use network home under macOS with Samba AD (Synology) fails with permission errors

We setup a Samba AD on a Synology NAS using their Synology Directory

Server. We successfully bound two iMacs to the AD. However, when logging

in, the login process hangs because of permission errors:

Application Specific Information:
Event history:
(
    "ACDServerCreateDirectory('file:///home/test2/Library/Accounts/') failed: Error Domain=NSCocoaErrorDomain Code=513 \"Du hast nicht die Zugriffsrechte, um die Datei \U201eAccounts\U201c im Ordner \U201eLibrary\U201c zu sichern.\" UserInfo={NSFilePath=/home/test2/Library/Accounts, NSUnderlyingError=0x7f99ffd09120 {Error Domain=NSPOSIXErrorDomain Code=1 \"Operation not permitted\"}}",
    "ACDServerMigrateDatabaseIfNecessary('file:///home/test2/Library/Accounts/Accounts4.sqlite') failed: Error Domain=NSCocoaErrorDomain Code=513 \"Du hast nicht die Zugriffsrechte, um die Datei \U201eAccounts\U201c im Ordner \U201eLibrary\U201c zu sichern.\" UserInfo={NSFilePath=/home/test2/Library/Accounts, NSUnderlyingError=0x7f99ffd09120 {Error Domain=NSPOSIXErrorDomain Code=1 \"Operation not permitted\"}}",
    "Error Domain=NSCocoaErrorDomain Code=512 \"Die Datei konnte nicht gesichert werden.\" UserInfo={reason=Failed to create file; code = 2}"
)
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Unexpected number of persistent stores (0), expected 1'
abort() called
terminating with uncaught exception of type NSException

The error occurs under both SMB and AFP.

Anyone any idea on how to get this working?