Over the past year or two I've had an occasional problem where my iPhone and/or iPad will not show up in iTunes via WiFi. Quitting/reopening iTunes generally doesn't help, nor does disabling/enabling WiFi on the iOS device. I can sync when plugged in via USB, but the only way to re-establish WiFi connectivity is to restart the device(s). This only happened maybe once every month or two previously, but ever since upgrading to iOS8, my iPhone and iPad exhibit this behavior much more frequently. I restart the device, which temporarily gives me the ability to sync via WiFi, but then the next day the devices vanish from iTunes (until I restart them again, then they disappear the next day, etc.). Anyone found a solution to this problem?