Noticed this same issue with my Nexus 5 on both 5ghz and 2.4. Also noticed on the 5ghz that it once connecting to it it doesn't always work or will stop working until I reconnect or just fall back to 2.4.Then, once in a while, my wifi will not connect to at work. I go wifi, tap the name of my work wifi, and it says "saved". It won't connect. I have my Lumia 520 with me at work also, and it is practically flawless with regards to wifi connection. Overall, the N5 is a very good phone.