When startup of stopped Virtual Host fails (for example, due to defect
QPID-8229) some of its children could be recovered and stored in virtual host internal data structures. The subsequent virtual host restarts can fail with another error "409 - Child of type XXXX already exists with id of YYYY". This error masks the original error causing virtual host failure in first place.
No error is reported into the broker logs. If original error causing first virtual host startup failure can be fixed, the VHN restart or Broker restart can give "409 - Child of type XXXX already exists with id of YYYY"