This is a known problem. I have it; I thought it was my fault for deleting too many apk's. Then a girl came along with unrooted stock phone and said she had it.
use app from play store to temporarily fix problem
My Note 3 drops WiFi at my home saying the signal its not strong, but my computer and the other phones can connect. I have to turn off cellular data to get it to connect.
Sent from my VS980 4G using xda app-developers app