JRASERVER-42282, executing requests to issue/createmeta on larger instances can take over a minute to complete and generate large content (500MB+).
The main problem with the old createmeta endpoint is that it is duplicating values in the response. Although the response can be filtered, due to the design of the endpoint it is very easy to cause downtime.
We have been working on a fix for this problem most of the solutions made the endpoint harder and more complex to use. So we decided to deprecate the old endpoint and introduce new endpoints that will replace the old createmeta endpoint.
Changes will be released with Jira 8.4.0 and the old createmeta will be removed in Jira 9. We suggest anyone who is using the old endpoint to migrate to the new endpoints.
You can find more details Createmeta REST endpoint to be removed
Note that old versions of Confluence uses this API, new version for API is used starting from 7.17.0. Plan your Confluence upgrade accordingly before Jira upgrade.