What trigger the hanging resources.. i don’t know. It’s pretty advanced stuff, and I’m not sure the answer is relevant to anyone else than r&d.
The real question (for the real world) is whether or not they have an impact on your admission control kpis. Do hanging resources impact your admission control in any way ?
As I told you, hanging resources are happening all the time (as far as i know), and -most of the time- shows absolutely no impact at all.