I've had a quick look at the Guard Scorpion script and it does have a lot of jumps (see those things with the "70" opcode?). By making the dialogue longer or shorter, you mess up those jumps so that they point to the wrong place (actually, it's like moving house and not telling anyone; your mail won't get to you any more), so whenever you do something like this, change the argument of the "jump" (70) opcodes that point to parts of the scripts whose address has been moved. You might be able to avoid this problem if you change the dialogue from "!, be careful!" to "It's gonna counterattack with its laser.â€" but keep the three lines the same combined length in bytes.
Actually, this might not be what's going on at all, but in any case it's good practice when AI modding to take notice of all the jumps in the script.