Whenever using a shovel or pick axe that breaks blocks very rapidly there is an occasional issue where the block disappears as if it were broken but acts like it is still there. You can't jump on it or run through it. You can't mine it. What you have to do to get rid of it is place a block down where the ghost block is and break that placed block. Sometimes, if you wait long enough, the block will eventually show up. You then can break it there as well.