Why is my Nexus 6 not detecting ANY wifi networks?

[AC Question]

Unlike most of the issues I see folks having with connecting to wifi, mine is different because my Nexus 6 is not detecting any wifi networks in which to connect. It just searches and displays "No Wi-Fi networks available". I know this is not true. It happens at home, at work, out in public...everywhere. Occasionally, after a restart, it will find and connect to wifi networks. But it is short-lived and eventually, the signal is gone and once again, there is no detection of any available wifi. It began a week or so ago. I do not believe I had a major update or anything. I did download the Cricket Wireless wifi detection app. I thought perhaps that was the cause so I deleted the app and have restarted the phone several times as well as shut it completely down since that time. I have also tried shutting down and removing/installing the SIM card. Still no luck.