In some AI package sequences I have, I have NPCs go indoors to do something (be it wandering around/eating/whatever), and then later on they need to come OUTSIDE for a bit. However it seems that, left to their own devices, they often do not come outside when they are meant to, they can only be prompted to do the correct thing (as according to their current AI package) if you enter the cell they are currently in or waiting for any length of time, whereon they resume doing what they were supposed to do (or if you waited, the game calculates where they are supposed to be without them actually having to physically go through the door to another cell, thus bypassing the problem of them staying in other cells)
My question is, how can you stop NPCs doing this thing where their AI effectively stops when they are in cells which the Player is not in, meaning that they do not continue with their intended AI schedule.

The things that might be happening
-The 'No low level processing' box is ticked at the npc.
-You've got too many npcs in one place
-You've used some script functions that disable AI-activity that prevents things from being processed outside of your own cell.
-You've not set the conditions right, or they'll never be met.