The exact same thing happened to me as the OP. I fought all the way from the beach too. Spent a great deal of time to push that stupid Ancient into the cave. Run up the ramp on the left side only to have some sort of game bug happen which sent a loud noise to my speakers and crash. Log back in, to the overflow of course, and no reward for all the time spent. Normally, it wouldn’t bother me so much, but that long “event” was just a zerg-fest of fortitude. Killing most things twice, especially the two champions at once, kinda sucked as far as excitement. Not really sure why I wouldn’t get an award after all that if you only miss the last minute or less.