Hiveborn Mobs Gaining Imunity

Several times today i encountered problem with monsters in Hive Fortresses (bat looking ones if my eyes are not mistaken) that remained on 1 HP and refusing to die. That bug started appearing when i paired Hive Fortress with Delirium Mirror. I also think this issue is connected to monster being permanently frozen (since my build freezes). It is quite annoying and failed several Fortresses because of it (totally hinders my build).