I'm using FmodEx long time ago, and fine with it up to now, I think your problem is because you copy all scripts have in demo, I only copy FmodEx (not copy Game_System *, Other Classes *), this will also cause error with other scripts that modifying the battle end scene, you must edit in that battle end script by yourself (by call some method of FmodEx into that battle end script).
About battle animation bug, just because def se_play, find this line in FmodEx script
def Audio.se_play(filename, volume = 100, pitch = 100)
FMod::se_play(filename, volume, pitch)
end
and delete it, I recognized that when I use "skill all", it will play multiple SE depend on the number of enemies (8 enemies, SE_play x8), and causes crash game.