My game crashes from learning Ice Slash as well. My characters are all leveled up legit. The savefile isn't an allowed extension to attach. Both Leanne and Chloe can learn Ice Slash. Might not be an issue with your patch, maybe it's the base game, but I'm not nearly ambitious enough to check. I do know Ice Slash worked in older versions.
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Maybe I can share the save file this way? Save data 2 3 or 4 are at an appropriate spot to learn Ice Slash, though the battle I'm saved next to is very hard for Chloe or Leanne, lol.