Don't use thread name with more than 7 characters (MISSIONCALL), the limit is just 7. For real you don't have need thread name (why you need this? Just put a 0000:)
Use random int opcode to get "wait" time for next hit squad instead of get 6 numbers and check. It will save lines of code and make it more natural. Also, random opcode with "0 6" also return "0".
You've requested models and at same time checked if all loaded, obvious it isn't loaded, it took seconds to load all of them, and if not loaded, you returned and marked models to be loaded again, and again... again... until load. You did a memory leak here, you don't have to mark model to load again (and again, and again... 60 FPS = 60 times each second). Just mark models and wait until it's loaded, don't need to load again
The mod will crash if any actor or vehicle is deleted. It will not delete easy because it's script controlled, but, you know, other mods.....
It's not so easy to crash if you just use good mods, but if you want to fix, just use 056D: 056E: opcodes after each "wait" while actors and cars exist, if some of them didn't exist anymore, immediately do something to stop all of this.
Your mistakes are the same as so many people do but that any good tutorial explains very well. Are you learning cleo scripting by decompiling script from other people? Stop this.
One of the best cleo scripting tutorials is by LINK/2012 here
(a bit old)(use Google Translator), but mine tutorial (using GTA3script)
is much more complete and well explained. From wait to memory handling.