I had the same issue today on a site with Kerberos authentication. It started after I extended the web app using Powershell. I was seeing the same errors in ULS logs as you have mentioned. For some reason the authentication mode for this web app changed from Kerberos to NTLM. I switched it back to Kerberos and the site loaded fine.  
Another strange thing is the authentication providers page for this web app has changed to SP2010 style, I'm on SP2016.
Please verify the authentication settings of your web app and revert it to the previous settings if you see any anomaly.