Structure: List item IDs must be unique
Within a single list, there can be no duplicate IDs. The IDs are used to resolve which child to render as the next item.
If you are not manually assigning IDs, it probably means that the title of two or more of your list items are the same, since the ID is inferred from that if not specified.
When this is the case, you can solve it by calling
id('someOtherId') on the list items that conflict.