Split off from T114043#1698940:
If you view a preview of a deleted board through the Special:Undelete interface (example) and scroll down to the bottom, the infinite scroll code will attempt to load more topics and get an API error back.
[FLOW] No topics returned from API [_RecursiveConstructor, Object, true, jQuery.fn.init[1], "window", "< .flow-topics", "flow_topiclist_loop.partial"]