since I've updated to 4.3 I have this problem on both stock and exisenz ROM. I use location based wifi and when it connects and I lock my phone and leave it there for some time (30 - 40 minutes more or less), wifi stops working. When I unlock my phone, the wifi icon is still there, but in fact wifi doesn't work. If I try to open google play, it says "No connection". To get wifi working again, I have to disable it and re-enable it. This is very annoying because I suddenly stop getting Gmail, Whatsapp, Viber notifications but I cannot know when.
Are you facing the same problem?