i got a fix for those who have problems with FSX. for me, the crash never reappeared. I did the same flight several times (EDDT-EDDF) and it crashed every time, then i reinstalled it in Network mode as Master and use FSX in window mode, then i did the same flight again 3 times and it didnt crash. I dont know if you have to reinstall it or just start ivap in external mode but thats how i did it. It could be related to FSUIPC maybe? Normally, i also had "Enable IVAP<->FSUIPC SDK" or something turned on in ivap settings, i didnt do that on my second installation. This might of course only be a temporary solution, but at least i can fly the NGX now (as i dont like to fly offline) Maybe this is worth a sticky until there is a real fix for that issue. A friend of mine confirmed that it works for him as well.

Hey friend, I've been experiencing this issue some times. Could you explain your re-install steps in details ? Did you uninstalled ivap first ?I run ivap-external and FSX in window mode, but the ivap crashes remains, not every flight, but still there. Thanks in advance

then i reinstalled it in Network mode as Master and use FSX in window mode,

Please can you explain what you mean by "Network Mode as master" ? Is this an IVAO thing with their software ?I do not beleive there is an equivalent concept with the two Vatsim Clients.