Though I'm not available to debug elevator problems, I can make a suggestion that has nothing to do with moving AI or trying new elevators or moving buttons, etc.
Back when St. Lucia was getting a facelift, the guards refused to use the small elevator in the mission. Nothing I did involving the elevator or guards would solve the problem.
Then I noticed that pathfinding, which likes to calculate distances and reachability between the centers of AAS clusters, was setting the center of a cluster at the bottom floor of the elevator high up on a worldbrush piece of door trim. Way up off the floor, and denying reachability to that cluster when evaluating a path with an elevator in it.
We changed that worldbrush to a func_static, and the cluster center shifted down onto the floor and the guards started using the elevator.
So here's my suggestion ...
1. Look at the rooms around each stop of the elevator. Filter out all entities, and allow monsterclip to be displayed.
2. Now examine all horizontal worldbrush surfaces (except the actual floor) and see if you spot any that don't have m/c sitting on them, extending up to the ceiling above. It's surfaces like these that dmap considers reachable by AI, and it will assign AAS areas to them. Cover these surfaces with m/c. (Or if the brush is a piece of trim, convert it to a func_static.)
3. Now make sure that ALL m/c in the room extends up to the ceiling. Otherwise, dmap will consider the tops of those short m/c brushes as walkable surfaces, which you don't want.
4. Dmap and see if the guards start using the elevator.
If not, I have no further suggestions.