I've had this problem for almost a year. When using WiFi with CyanogenMod 11 (Android KitKat 4.4.4), the phone lost connection to WiFi and no data came through even though it looked connected (the phone didn't use mobile data, because it was still connected to "faster" WiFi). Some apps drained the battery even more waiting for data and keeping the phone more awake (mostly waiting for position acquisition using Google geolocation).
The problem was caused by WiFi router configuration where I use latest OpenWRT. The damned WMM mode (some special kind of QoS for multimedia) was causing this, and after I turned it off, there were no more lock-ups. From what I've read, there is a bug in Android sources that causes this and nobody bothered to fix it so far.