That’s a great question! Just to clarify, is there any chance that you have multiple assignees when querying like this? To confirm, that is currently the expected behavior, as items_by_column_values will not work for columns with more than 1 result, like the People column.
@JCorrell thanks for jumping in here! I’ve just tested this further on my end and this does work for an item with 1 assignee but doesn’t seem to provide any results for items with multiple assignees, unfortunately. But it does do the trick in general