We updated our magento 1.9.3 to 1.9.4 (via connect manager) and also updated our PHP to PHP7.0 Everything seems to work fine and our site is much faster.
But now we have strange problem. Sometimes our site freezes totally, for example when going to checkout, and nothing helps but closing browser and emptying browser cache. Same time it works fine when you open our site at another browser. Fortunately this is not happening so much in the front end but more in the admin when we place to order and all the time when we use our POS system. (that is X-pos, nowadays called http://www.connectpos.com/). I think POS extension is not the reason for problem since same happends without using POS. But with X-pos we can make 1 or 2 orders and then it freezes. And if we try to reload page or go to admin browser cannot get any bite from the site - not traffict at all.
Any ideas what could be wrong? Could this be something to do with sessions? Maybe there happends some error and magento locks session for some reason?
We tried many things but nothing helps. We have updated extensions, but no help at all. We have asked help from some extension developers and they just goes to our site and says: hey, everything seems to work fine. ANd it does, until... it freezes again.