A Vault document remains in a transitional document state and the workflow completes unexpectedly.
The workflow contains a decision step which is configured with an unhandled else decision rule. If there is no match to the decision rules, the workflow sends the document to the else route. If the else criteria is not handled, the workflow ends leaving the document in the current state.
An orphan route is when the next step after the else route is the end step of the workflow. Be sure else cases are handled properly for decision steps. For example, use a state change step to put back the document back to its initial state in which the workflow was started.
Vault Help Documentation: Configuring Document Workflows: User Task & Decision Steps