I would take a look at the Communities post When you create a sub-task can you automatically inherit certain fields from the parent for the way others have resolved this issue in their instances:
Here is the advice from one user:
"In the create issue transition you can set the "Set Field Value from Parent" option in the post-functions. You can either do this in the default workflow you are using for the project, or make a separate workflow for sub-tasks. When only using this post-function, changing the value of the field in either the parent or sub-task will have no influence of the others value."
In addition you can also try Automation for JIRA.
The Jira Marketing team is putting together an ebook on migrating to Data Center. We're looking for pro tips on how you staffed your project team and organized your Proof of Concept. Share yo...
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