The mod used with this game was Altarn's Polished Twilight of the Arnor 2
What is going on here? I never had this problem before? Is it something with the mod or my computer?
In APT2 several weapons (even missiles and mass drivers) have the following tag attached to them:
I'm not familiar with that one, and it isn't in the vanilla GC2Types.xml. So, it's possible that this and your issues are related, but I'm not 100% sure.
Could you start a game without using the mod, and see if the same thing happens again?