We recently fixed a bug that was stopping events from the Event Data Crossref source making it into our Scholix endpoint, see for example this API query. The fix works for new events but we need some further work to backfill for previous events. We are working on this and expect it to be fixed in the next couple of weeks.
Scholix and support for data citations remain a high priority, and we are working on adding all reference data from the Crossref metadata API into Event Data - including data citations. You can track this and other Event Data projects on our public roadmap.