REST API - Missing abstract in submission

We have a OJS installation and have some additional “pages” showing submission informations.
Now I want to show the submissions abstract text but the API does not return the “abstract” property (as part of the publication element) as described in the REST API documentation.{submissionId}/get

Does anybody have an idea what could be wrong?

Thank you

As I have now noticed, there are more fields missing from the REST API response. In the “publication” element of the “subscription” object the “issueId”, “keywords”, “language” and “lastModified” are also missing