although they are called hard pellets,they do still contain oils,and flavourings which will dry out and start going stale,which makes the pellets less dense and more airey as they dry out,and so they start floating.similar to groundbait when it dries out or contains too little water to dampen it down properly.

I don’t know if they have changed the mix for pellets but I am finding more and more instances of hard pellets floating. This is especially if they are kept in bait boxes or after a full bag has been opened but not fully used. I now soak them before use, just add water then tip it off. Even then I have had instances of pellets not sinking so I always check them.