How are you creating the relationship between the Item__c model back to the Events__c model? If you are using a “field from another model” condition the “Event_c relation” field will be auto populated with the same proto ID that is used in the Event Model.
Secondly - how are you saving? You should have a page title component with “Events__c” in context. The Save and Cancel button should have the “Item__c” model as “additionally saved”
Finally the model order should be Events__c and then Item__c. You can drag and drop models in the model list.
Let me know if all that helps.
