The thing that's happening here is that you try to read the data of a monster that has a NONE AMP reference. It's specifically being done in the block that creates the enemy battlemonster objects.
From what I can see, the issue happens when you start a horde battle without generating enough monsters to fill all enemy horde slots. (This is why it works in 1v1 battles - you always generate 1 enemy monster so creating 1 battlemonster will avoid reading outside the available data)
Should be simple to solve, at least. Wrap this block
in a copy of this condition
and it shouldn't try to read the unset data anymore. (Note how the inner block also changes the monster state from "DEAD" to "NORMAL" when doing this, which will also lead to issues down the line even if you ignore the data reading bit - this is what causes the second crash)
