I am facing very same problem on lumia 435 dual sim. The mobile data is not turning on and when i press the short cut button on the drop down menu the phone hangs and then it needs to be restarted and when i try to open cellular&sim settings from Settings>NETWORK & WIRELESS the phone hangs again and then only restarting the phone will make it to responsive. The very same problem is with Wifi button as well with very little difference as by pressing its shortcut button in the drop down menu or from settings it does not hangs the phone but some times it finds the wifi network and some other time it does not find any wifi network even when the wifi signal are very strong. and only restarting the phone makes it connect with wifi.
Any workaround for the above mentioned problems will be highly appreciated ???
Microsoft what sort of engineers and programmers have you hired to make OS i mean it is more than an year or so and still OS is buggy very buggy indeed. if you continue with this sort of progress i suspect in next 100 years or so Microsoft will eventually be able to launch its mobile OS just set aside the problems with OS8.1