New customer account - Customers lose their login

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Since last week our customers have been reporting a lot of problems with logging in to our store, they log in but then when they return to the store and start browsing the store they lose their login and are forced to log in again, we have cases of customers logging in more than 4 times and ending up giving up because they can't, it's some problem related to shopify Customer object, somehow the object disappears after the customer changes pages.
Any suggestion?