add to cart problem / cart session problem

dear friends,
1st problem : We add proudct to cart in product detail page. Then we go to other product pages or categories and see that cart is empty. Sometimes chart comes empty only in the next page and sometimes a few pages after we add the product to the shopping cart. It is same with Chrome and Firefox in my android mobile phone.
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2nd problem : after I add a product to the shopping cart I wait and see that other products are also added to may cart without my control. Number of products goes up and down, but I am doing nothing. It means some other visitor is adding or deleting product and I see the actions in my chart.
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can you please advice us something to solve this problem.