After installing this in P3D with the Estonian Migration Tool, I proceeded to rename the trafficAircraft.bgl file to trafficAircraft.bgl.ORIGINAL, so that the default AI would not show up with the new ICE AI traffic.
After the second time I got the error, I uninstalled ICE AI Traffic and renamed trafficAircraft.bgl.ORIGINAL to trafficAircraft.bgl, did a flight and low and behold, now I did NOT get the ACONTAIN.DLL error after landing and pressing CTRL-F12.
That thread discussed the same .DLL but, if you read it to its completion, it didn't had anything to do with GSX, both because the poster said he had the crash as soon as he went near KDFW (without activating GSX), but also because that error was a KDFW-specific bug, an object name was mis-typed, and while in FSX this is mostly harmless, in P3D it causes a crash.
From your description of the problem, it's only happening AFTER you press CTRL+F12, so it doesn't have anything to do with the above thread, even if the crash "looks" the same.
As I've said in that thread, there's only ONE place where GSX interacts with ACONTAIN.DLL, and it's the feature that removes static ground vehicles near the parking when you select a parking to be used by GSX. Now, this would happen only AFTER you select some kind of GSX operation, like Boarding, Follow Me, etc. NOT "just" by pressing CTRL+F12. If you only press CTRL+F12, there's no interaction between GSX and that .DLL YET.
So, it's really happening *immediately* after you press CTRL+F12, or you are able to select a GSX operation and THEN you get the crash ?
I am going to re-install ICE AI Traffic and see if I can reproduce the error once again. If it does CTD again, then I know for certain it's the AI package that's causing a problem when activating GSX after landing.
Same as with the KDFW bug, where a mis-typed Simobject name caused such crash, it's possible the crash is JUST caused by a similarly mis-typed Simobject that is used as an AI of that package. This won't be noticeable in FSX, the AI would simply not appear, but it causes a crash in P3D.