I’ve noticed a serious MSFS engine AI traffic limitation. This problem happens ONLY when you are doing more legs in the same aircraft. Let me explain.
You spawn at your airport lets say Miami KMIA. You are going to fly to the New York KJFK. You spawn at the gate, start FSLTL injector, it injects traffic everything works fine. Then you fly to NY. AI aircraft is there, AI aircraft is moving, landing, taking off in New York - everything works fine. Problem starts when you decide to continue (no game restart, no going back to menu) from the New York to anywhere. For example you want to fly back to Miami KMIA. At New york it still works fine as it should. Planes are landing, taking off and taxiing. BUT in Miami there is not single aircraft spawned, planes are not taking off and planes are landing only, but 10 seconds after touchdown (according to the fsltl traffic command prompt log) they are removed by MSFS engine (no explanation like for example out of range). Restarting injector does not help neither removing traffic. Only fix is - going back to menu/restarting game and start over from the scratch - spawn again at the gate let the game load again.
TLDR - if you want to fly more than one leg in one game session aircraft wont spawn at the 2nd, 3rd 4th, 5th etc. destination airport no matter what you do.