Update (7 October 2022).
In order to give our Marketplace partners a better experience in testing Change 6 (changelog items in webhooks), we decided to change the rollout plan for it to return both OLD and NEW changelog items in the SAME webhook event. Originally we announced that we would only return either OLD or NEW changelog.
We plan to rollout Change 6 to Early Adopters / Jira Ecosystem Beta group, and later to all other instances, within a month from now. We understand that this may not allow enough time for you to test your changes. We will monitor the usage of the old fields, and we will switch them off at any point after 30 Nov, when our monitoring indicates that it is safe to do so. If you think you won’t be able to make the required changes to your app before 30 Nov, please let us know.
The bug [JRACLOUD-78657] Inconsistent rest api behaviour when setting parent issue when epic link is not on update screen - Create and track feature requests for Atlassian products. will also be fixed before 30 Nov.