What Limits Selectable Users When Setting Task Owners?

What Limits Selectable Users When Setting Task Owners?

Hello,

I've recently come across an issue where we're unable to see all the users that are assigned to a given project when selecting them as Owners of a Task in the drop-down menu.

This is not the case for all projects and tasks, and I'm unsure as to what settings might have been tripped here.

What limits the list of available Users when assigning Owners to a Task?

Thanks,

Lee