I'm not entirely sure how this could happen, but I did see a hang occur due to a loop where an app was polling a query status, and we were trying to wait for a fence value that wasn't associated with a command list (i.e. no actual commands were recorded) but the fence hadn't been signaled yet, so the wait was never satisfied. I suppose an event query is has no commands associated with it, so this could happen there.
I'm not entirely sure how this could happen, but I did see a hang occur due to a loop where an app was polling a query status, and we were trying to wait for a fence value that wasn't associated with a command list (i.e. no actual commands were recorded) but the fence hadn't been signaled yet, so the wait was never satisfied. I suppose an event query is has no commands associated with it, so this could happen there.