Subprocess not returning to parent process

DO you have 2 end Nodes in your sub process?
If yes, the flow in which it got executed, has the terminate event?

I am also having similar issue what is this terminate event?

I am also having similar issue what is this terminate event?

An End Event is used to denote the end of a process flow within a process model. The process remains active until all active paths in the process arrive at an end event.

If your sub process have multiple flows towards end event. In such case make the end event from the configuration of the end event node.
Steps:
Open the Configure End Event dialog box.

Right-click an End Event on the Canvas and point to Results. The Setup option appears. Click Setup. — or —
Double-click an End Event on the Canvas.
Click the Results tab.

Click the Terminate Process link. A Terminate Process row is added to the End Events list.

(Optional) Type a name for the event in the Name column.

(Optional) Click the Configure link in the Setup column. (This link changes to Edit, if the trigger was added previously.)

docs.appian.com/.../End_Event.html

Hope this could help you.