I noticed this problem a few weeks ago. For some reason, my phone (N9005) has no problems connecting to my home WiFi and a few other ones that I have saved, but when scanning it doesn't show any other WiFis except the ones that I have saved, it's like it isn't even scanning. I tried to delete my home WiFi off of the list and sure enough, when I scanned it was completely gone and the phone couldn't see it. And then I manually added the network and it connected without a problem.
If anyone has any input on why this could be happening, it would be greatly appreciated because it is a huge pain in the ass, especially when you're out and about. Thanks in advance.