This shows the issue - unless all of the chunks between target and launcher is loaded sometimes missiles get stuck mid flight until they get loaded. I had tested this several times and it does not make any sense to me. I launch them from always loaded spawn chunks (on video there supposed to be 10 rockets per 10 salvos ) and it sometimes work and sometimes doesn't.

I have tried (500 to 1200 flight distance on render distance 16):
(missile count, source, target - works / does not work)

1. single missile, chunk loaded by player, chunk unloaded - works
2. single missile, spawn chunk, chunk loaded by player - did not work once at 800
3. multiple missiles, chunk loaded by player, chunk unloaded - works
4. multiple missiles, spawn chunk, chunk loaded by player - did not work once at 500 and 1200

I have to point out that I have no idea how this mod works so this is pure speculation:
I noticed that missiles take two kind of paths:

1. low - if the distance is not far enough they fly closer to the ground being visible entire flight
2. high - if the distance is greater then they fly almost vertically to vanish in the sky and spawn again in the vicinity somewhere above the target

If they take the high trajectory then I never have any problems with then but sometimes it seem that they take low trajectory even if the distance is big enough and they freeze on unloaded chunks.