We're aware that there have been issues with the current epic boss Emperor Xhao. We have released a fix to allow attack bonuses to work correctly with epic bosses, but a few issues have cropped up. A fix has since been deployed and everything should now be working correctly.
Unfortunately the goal for this epic boss has been corrupted for many of our players. At the end of the event we will manually award all players who have defeated the epic boss 35 times. If within a few days of the events conclusion you still haven't received the reward in your inventory, please contact us via the in-game contact button.
Additionally, epic bosses are now set to not reappear after every attack. There is a percent chance of triggering an epic boss which is working as intended.
Finally all players will receive an additional reward in the coming weeks via a popup in game.