First Available Does Not Always Show a Task

I have various perspectives in OF, and for some it makes sense to use the First Available Feature because it actually shows available items, but for others, even though I think there are available tasks, OF does not think so.

I have set up the perspectives that work with First Available and those that do not with First Available in the same way, so I am not sure how First Available works. If anyone can clarify it, I will appreciate it.

Here is an example of how I have set up the perspective that works with First Available:

Project Hierarchy: Don’t use
Presentation: Ungrouped, Duration
Layout: Custom
Filtering: Any Status, First Available (or available,… which ever shows a manageable chunk of tasks), any duration, remaining
Focus: I have selected the appropriate project folders
Sidebar selection: sometimes I have contexts selected, sometimes I don’t