I found a new bug after this update. The missions which need special hero are reset to zero star status. May you check this. BTW, ice demon bug is fixed, however, when finished 1 map of ice demon, one hero is stucked and not moving. But it's ok when i redo the mission.
Candle is right. If you increase party level, your all heroes will increase their HP. But i think damage and defense all depends on gear nothing else. So what benefit from each hero level up ? i believe only skill point increasing. From this conclusion, low level hero increases their level may help whole team than high…