Process instance does not become Completed state even though all the nodes in the process instance have completed by triggering the failed node.

Issue

I have a process with a process definition like below.

Start node --> REST Service Task node (with "is Async" flag enabled) --> End node

When I started the process, RuntimeException occurred in the REST Service Task node above because the destination REST server was not running. After I got rid of the problematic situation by starting the destination REST server, I clicked the REST Service Task in Process Diagram pane in the process instance page, and then triggered the task using Trigger button. However, the process instance did not become Completed state (still be Active state) even though all the nodes in the process instance were completed.