I already searched for a while but I couldn't figure out any answer.
My customer got a problem for a long time with his shop. First of all I thought it's an personal problem of his browser/computer because no one else got this problem. No I realize it is hard to reproduce and happens only under special conditions.
Our Magentoversion is the 126.96.36.199 with all security patches applied.
When the shopping basket is left for while. Magento sets at the visit a cookie called "persistent_shopping_cart". So first off all for the shopping cart itself nothing is wrong with this cookie, but over time some product pages wont shown that customer anymore. He will get a 404 error instead. I couldn't figure out how the selection is made but after a couple of days (cookie is set) some "random" product pages return a 404 error. This error only happens to the customer which has that cookie set on the browser. If he access with another browser everything works normal. The product pages will shown without any problem. Refreshing cache and reindex data won't fix that problem. It also can't be fixed by clearing the general browser cache.
But when I delete this cookie, all problems are gone and everything works fine again for that browser.
May you can help me.