When the Shipment Confirmation process attempts to identify an eligible manifest, attributes for the shipment leg and prospective manifest must be in agreement.
If a compatible manifest is not identified, the process will get a global lock on the Manifest Lock table, then re-query for a matching manifest. If match is still not found, then a new manifest will be created and the global lock will be released. If multiple threads try and acquire the lock, they will be serialized.