After checking code, error "STR_NO_USES_LEFT" can only appear if you use new instant medikit and you run out uses.Did you use "RandomType"? this change how damage is roll.
I don't even know what the instant medikit is; and never used "RandomType" anywhere ever. I just switched to Extended, and the -literally- only feature I'm using is the one for overriding the alien base construction. This is the medikit in question, it is the exact copy of the vanilla medikit (changes marked with "**"):
- type: STR_MEDI_KIT2
size: 0.1
costBuy: 3500 **
costSell: 2625 **
weight: 5
bigSprite: 464 **
floorSprite: 464 **
handSprite: 464 **
battleType: 6
invWidth: 1
invHeight: 2
painKiller: 10
heal: 10
stimulant: 10
woundRecovery: 1
healthRecovery: 3
stunRecovery: 4
energyRecovery: 10
tuUse: 10
flatRate: true
1) I can't reproduce it. Can you test it with F8 that will slow animations?
See attached images. Taken with slow animations activated. Left launcher has 2 missiles, right has 1. As you can see, none of them gets drawn at all, you can't see anything flying towards the ufo.
So the issue actually is not that the first missile isn't drawn, but that during the very first seconds of air combat *nothing* (the cannon doesn't seem affected though, only missiles. duh, this is so strange) gets drawn.
-- edit: it also seems, to me, that the "invisible" missiles don't do any damage/never hit the ufo.
In the following days I'm going to switch back to vanilla OXC to test on there.