Backpack disappeared?

Is there a set timer on how long you have to recover your backpack after dying? I've noticed that if I save and quit after dying, my pack isn't there when I go to recover it. So I just died while attempting to clear out a weapon base on Akua, waited until it was light out to run and pick up my pack, and by the time it was dawn, the pack was gone.

Is this a known issue or am I missing something?