Steps to reproduce:
1. Let opponent set up an Active Zygarde-GX with less than 150 HP remaining, and no other Pokemon.
2. Let Zygarde-GX use its GX attack, rendering it immune to "damage" from Xerneas-GX's attacks.
3. Use Xerneas-GX's GX attack, transferring all of Xerneas-GX's damage counters to Zygarde-GX.
4. Observe that Zygarde-GX is Knocked Out, logically ending the match -- but the match freezes, and the result screen never appears.