This has already been reported and is under investigation by the devs.
Most players reporting it have Ironhawk (or Queen of Sin) and a troop or weapon that targets a chosen enemy, the hang happens when casting a troop/weapon that requires an enemy to be selected but Ironhawk kills all enemies first. In your case, I’d expect that it could happen if you cast Chalcedony, but you should be fine if casting Mountain Crusher.
One player has reported seeing the same sort of hang with other teams, apparently randomly.