This is due to the fact that one of the enemies in the group of monsters was too far from the player's party. By default the monster is limited to 10 cells when moving. If it cannot reach the player in 10 moves, it will stay in place and skip the turn. If the enemy was hidden or unable to move because of the in-game obstacles, this could lead to the player never leaving the combat, since the event that should lead the enemy visible cannot start.

Now the radius of movement of aggrieved enemies is increased by three times. If all enemies in the group have skipped the current turn and are outside the aggression zone, the player's party will automatically leave the combat.