Hello Vinesh !
Check either of the reasons hold:
1.As Anjan pointed, whether the method awaits for any terminating event.
2.The method has raised exception.
3.Whether the containers have been populated with required values.
4.Debug the method and verify any discrepencies refrains the method from successful
execution.
5.Ensure no user is trying to manually create position or missing dependency data
related to those position creation is deleted.
Answering to above questions by Anjan,Rick and Abhishek also would narrow down the problem. Because, missing authorization to the back ground user, missing RFC configuration, verifying whether other instances of this workflow is also affected or other workflow's instances also affected etc can be suggested.