Game: Die Reise ins All
Savegame: Save07.zip
Continus Player build

In this final boss fight, the character Heisen is temporarily removed during the 3rd round. This is a bit hard to reproduce, because it depends on RNG, but you can use Auto-Battle to quickly spam through Round 1 & 2.
Round 3 will start with some dialog, causing the last party member Heisen being removed. But because the attack targets seem to be calculated prior to the script execution, the boss may have targeted Heisen's party slot with their attack.

The dialog of the 3rd round is over when this message pops up:

Right after, the remaining party members execute their attacks and if Heisen has been targeted previously, EasyRPG Player may crash on trying to execute the enemy's battle action on an invalid target.