Aha! Feature may contain Requirements from different Jira Projects. Right now, the fixVersion is synced with "fixVersion ID", which will not be synced successfully when the Feature (Epic in Jira) and Requirement (Story in Jira) belong to different Jira projects.
The status of this idea was out of date. It is now possible to keep records in sync correctly when the parent record lives in one Jira project and children live in another. This article explains how to set this up in Aha!