What did I do wrongt?

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I put up bread and butter pickles this past week, of course, it wasn't the first pickles I had put up but it was the first time my pickled floated to the top and left space at the bottom. I cannot figure out what I did different. I packed them hard and then put in canning bath for the time I needed to. Does anyone have any suggestions as to what I did wrong? They taste delicious and look so pretty but I don't like them being at the top and just seeing juice at the bottom. Any help will be greatly appreciated. God bless you!