An enemy duo left, but one of its players is still considered to be in-game. During the recruit phase, the player is shown to have 0 health and X armor (depends on how much damage they took last combat). At the start of every battle, they’re fully healed. We technically won this match, but this bug got us stuck in an infinite loop so my duo partner eventually quit. Link to screenshot:
https://imgur.com/a/abcXewN
EDIT: I decided to leave the game on autopilot in the background while creating this post and doing some other stuff, and apparently there’s a turn limit, because after the Nth combat my hero portrait exploded and the game ended by itself. If you need to check the match in question, the battle tag is Soryo#11922 and the match is the last one I played.