I've just disassembled it and reassembled again. Everything looks good. All connections are good and nothing seems to be loose.
I even tried to press the back panel around the camera lens to make a better contact with the antenna, but still nothing.
Looks like this in the WiFi settings...
So, actually, I think it's a software problem and am going to root it now and flash the new ROM.
After that we'll see.
If there isn't any success after that, you all know where to find spare parts for your Nexus 5.
Sent from my Nexus 5 using xda app-developers app