I updated to a Nexus before I had a Moto E. I am able to sign onto wifi at home but once I’m at work I cannot. It seems to be something with security which was never a problem before. Maybe more advanced settings now. In the past after clicking on the network a webpage would show and I was able to sign in. Now a webpage shows up but it says “The network your’re trying to join has security issues. For example the login page may not belong to the organization shown”. It gives the option to continue anyway via browser. When I click that another webpage shows up and it states "Your connection is not private attackers might be tring to steal your information form 184.108.40.206 (for example, passwords, messages, or credit cards). NET:ERR_CERT_AUTHORITY_INVALID. At this point I have two options “back to safety” or “advanced” I thought it may have to do with the data saving setting so I turned it off and tried without that running. Still the same screens showed up.
This is the message you get when a captive portals security certificate is invalid/expired. I get this at work on our guest network. If you trust things are OK otherwise, hit the “advanced” link.