Android Doze drops Wifi regardless of optimalization settings

My LG G3 with Android 6.0 uses the built in Doze mode to save some battery. At the first setup, I set applications to ignore Doze mode (like chat apps, Gmail, Viber etc.). I also set the "app" called Wifi to make my Wifi enabled while in Doze mode. They worked okay, I get my messages even if my phone is in Doze mode. After 1 year of usage, when I unlock my phone, I can see that my phone is switching from _mobile data_ to _Wifi_ and my data package is being used up by the aforementioned disabled programs. Why? And how can I make my phone to use Wifi permanently? What changed after 1 year?