I have found a possible solution!
The problem has caused most probably by errors in RMP files in non-genuine UFOs.
Some time ago, someone said that distances between nodes in routes maps are not things to worry about. This is not true! I have noticed that if zero is set as the distance between nodes, OXC may crash during an alien move (if this map is loaded). It is because an alien wants to move, and the game cannot count the distance. For some reason, either negative or more than 255 values appear, and this causes the crash.
The original game seemed to be resistant to such errors. Unfortunately, OXC is very sensitive in this point, and our otherwise great coders (many thanks for OXC!) said that they would not deal with it, and delete this problem as a bug. So, it is modders who must repair their maps instead...
What is a solution?
The solution for NOW: If you play a campaign, and just want to finish the battle which constantly crashes, you must edit your save. Find all alien units, and set their morale to 0. Your battle is practically won - but this will prevent crashes. It is so because alien units will not move on their own, only when panicked. If you make several turns, and the game will crashes again, you must edit again the save.
The long-distance solution is to stop playing Luke's Extra UFOs and/or Final Modpack (cause both contain wrong RMP's) until new versions will be ready. I am about editing them and make them work all right but it needs much time... If you cannot wait, use MapView and replace all naught-distances with their true values. MapView 1.12 can make them automatically. It is a very tedious job as you must check each node one by one... So better wait for a patched version of your mod.
Anyway, I have checked that this is a real problem. Parhaps thera are other reasons for game crashes - if you find any, write about them.