The Cain battle, unfortunately, is back to throwing error messages (and every single other battle too) on 19.5.18. I don't know if it's even possible to get earlier versions of Reborn, but I have genuinely no idea what's happening with it. The battle AI seems to be doing something odd that then results in the sprites vanishing
Update: I'm getting this bug on base 19.5 too, re-extracted the game to check and it's messing up there too.