Can someone explain Private Locker mechanics to me?

Hi Everyone, thanks again for the help with The Network linking struggle I was having. So it’s very frustrating when I put a lot of great things I need later in my locker, and when I open a private locker it’s not there. Are these things location bases? Why can I sometimes see multiple on one locker?

Bonus: why does Sam in his private room shake his head when you hover over the door leading out, and nods his head when you pan over to the Terminal ?