I'm encountering a bug lately in the story event wherein a particular unit seems to try to take an action but fails to do so, this soft-locks the battle and the enemy becomes unkillable.

The setup

1. CG Protagonist who auto-fills LB first turn (in this case, Firion), paired with Upgrade Package (A.I.Katy STM, which has a before-turn activated passive)

This is the only discernible trigger for the bug I have encountered so far. I have not tested for cases outside of this however.

The effect

CG Protagonist greys out, Repeat and Reload commands grey out. Enemy becomes unkillable (stuck at 0% hp) and ally actions can cut short similar to an enemy dying between attacks.

The Solution

Closing the application and re-opening. There will always be a download of around 0.015mb. This will bring you right back to the round you encountered the bug on so it's simple to continue from there.

I will be filing a ticket to support and encourage people who have encountered this bug to do so as well. It is an inconvenience but might not be too widespread.