REST2 Delay Or Caching?

I added a child ticket to a parent ticket. Then I call REST2 api with parent ticket_id, the result is not updated, there is no child object in ticket’s return _hyperlinks. So I call again. At that time I get updated data. Why is it happening in Request Tracker REST2 ?

Were there any scrips running as part of the creation of the child ticket?

I think there is no. I just created two tickets. Then, I link one to another as parent.