I just saw a tweet from NYSE saying that trading has resumed. But I think this is too late for index funds so they might not be filling orders because they don't have pricing (or didn't have it when their systems needed it, which I think is by 11:30 eastern).
I'm still waiting for the buying opportunity that I thought was going to be on Monday, but I think this is not the day to be trading (you would have to wait until you were sure trades got cleared).