Samsung S4 WiFi Problem.

I have cm 12.1 on my s4. Recently after rooting it with cf auto root. I find when I connect to WiFi. Then it automaticly disconnects and then I can't reconnect. I have to enable and disable flight mode and then it sometimes works. Help please
I have tried reflashing the ROM version I first use when using CyanogenMod. Please help. Can't find answers anywhere