When i destroyed the enemy shrine with a circus deck containing Ethereal pool, the timer did just keep going and i had to close the game because i couldnt get out of it. and when i got back i couldnt play that encounter again. Daily Skirmish testing again against the next PvE. noticed circus decks still work in daily PvE, its probably just custom PvE it dont work in. Same problem in the next PvE i tried, i can see the shrine explode and then it just keeps going on...
I don't know if this is a bug with Ethereal Pool specifically, or anything that causes the AI to lose on its own turn. I had the same bug, but its trigger was defeating a boss with the damage from Frost Aura.
I have successfully beat the AI with Ethereal Pool, match ended and received rewards. Have also had it hang several times. Not sure what may have been different in each case.
This isn't a PvE only bug. As i've had it happen to myself when facing other players. The game will end up being recorded as a victory but you'll be forced to exit your client and restart due to the freeze.