I tried it again and this time the error didn't occur.
But well... this game was quite entertaining and well done but now I had to finally quit playing in the volcano. It seems like there's no way to harm enemies in there. Living Flames and Lava Fiends absord nearly EVERY damage (except for Suven's for some reason I don't know about). Even if I break their Fire Shield using Ice Magic, they keep absorbing any physical or lunar attack, so Tilana -in both states- is completely useless against them.
I can spawn the blue form of the witch to have some ice skills but they inflict 7 (!) damage to them, so Suven remains as the last actor that has at least one ice skill that does damage to them. Last but not least, these things heal much faster than I can inflict damage to them.
I had a pretty hopeless fight lasting more than 15 minutes for one single random encounter until I decided it's the best to escape the battle and immediately escape every other random battle including fire enemies. Pretty much every skill that does damage seems to be quite useless as I can't find a way to stop them from absorbing every single hit. I had to read through my whole skill set for several times but still I haven't managed to beat any of them.