Negan said:

The grade 1 champ with a max level of 15 sent 664 attacks, far after it was maxed out at level 15. I lost a lot of emeralds and had to manually stop the hunt because it continued to go.

http://prntscr.com/nw4blp

Hi. Make sure on Solo hunt next time to set up attack limit (can be activated under the recharge energy option on Solo hunt page). If not set, it can go on until you run out of recharges and emerlads. Hope it helps.

this is not a defect if you read the guide it will show you that's how they were meant to work. Group hunt can be used on individual hunts they will stop when champion is maxed  but solo with recharge will just keep going until the energy and Emeralds are gone unless you set it to stop