I'm helping a developer of an app post this on their behalf. Can you please help out with this?
When adding items to personal lists, after the POST request to add an item is successful (the response returns added.shows = 1), this change is not reflected in the GET request response to fetch the items of the list right after. It returns the old list without the newly added item. However this fixes itself after 5 minutes or so.
This is likely due to the HTTP cache is not invalidating quickly enough returning a stale list of items.
Please let me know if you need any other details and i can work with the developer to get it.