I believe that the problem is that you are storing the CSS position of the elements. The sortable widget does not modifty the CSS offset, instead it reorders the elements in the DOM tree.
In order to restore the previous position you should render the elements in their last order. In other words if the user has moved item 1 after item 2, then when the page is reloaded the HTML of the item 1 should be located after the HTML of the item 2 in the DOM tree.
For your convenience I prepared a small example which demonstrates how to store and render the items according to their last position before the reload.
The example uses kendo.template to render the Sortable items.
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