Suggestion

When creating sub task from a parent task, it should copy the Fix Version from the parent issue.
Additionally, when the parent's Fix Version changes, the sub-tasks' could change as well.

Steps to Replicate

1. Create a test project
2. Create some issues
3. Create some version
4. Assign fix version to one of the issue
5. Create subtask

Expected Result

Subtask created with Fix Version populated

Alternative solutions

Workflow

1. Add post function in the create transition, (select the text mode > select the first step > you will see create transition on your left)
2. Select Copy Value From Other Field
3. Click next, select FixVersions as the source field and destination, for the option pick copy from parent
4. Publish the workflow

Automation Rules

Configure Automation Actions that allow you to achieve this.