For some reason, every time an aircraft is asked to line up and wait, or exit next intersection after landing, my AI at the runways disappears after I've been given the green light to land. That's the only place I see it happen, because you can see every other traffic parked or taxing around the airport.

Just a guess, but i think it's VOXATC way of clearing the runway after giving you clearance to land. My thoughts are that VATC can control the AI, but it cant control you in as much as exactly how long, according to your preliminary and final approach speeds and therefore exactly when you will be landing, so if you get there a little quicker than VOXATC estimates, there's a 747 taxiing or sitting on the runway. I assume this is what you mean?

You're probably right, but I was coming from a good distance on a Cherokee 180 at pretty slow speed. I noticed that the plane that had landed was given the instruction to vacate the runway at the next turn, but it just sat at the runway without moving. In the mean time, ATC orders another aircraft to line up and wait after giving me the okay to land! Why would it do that when it should have ordered that aircraft to wait since I was coming down for landing? Just to let you know, I have my FSX traffic sliders down to zero on both heavy and GA. I keep VoxATC traffic at 50%.

I noticed at Fly Tampa Dubai that AI aircraft, when managed by VoxATC, were lining up on the runway, then doing nothing, then eventually disappearing suddenly. The same aircraft managed by default P3D (and presumably FSX would be the same) behaved properly. I eventually tracked this down to a problem seemingly with the taxiway geometry; if AI had to negotiate a tight curve onto the runway, this seemed to cause them problems. When I deleted this tight curve, so they were forced to use an alternate and more gentle path to the runway, they behaved properly.

 

I'm still not sure what the fundamental geometry problem was, but it may have a bearing on your experience.

I have to check other airports, but I first noticed this problem at my local KMCI airport in Kansas City. There is no tight curve to enter the runway, but I believe that the aircraft that had just landed, stopped next to a 90 degree turn intersection to taxi off the runway, and that is where he got stuck. After sitting there so long, and since I was closing in to my final approach, both aircraft then disappeared. I'll see if it will do the same at other airports that have that 90 degree tight turn, and check back.