I have tried everything to solve this problem with my S7 Edge. Today I acessed my router and found it was 2.4 and 5 ghz. when AT&T installed they changed network password for me, but only for 2.4 ghz, the 5 ghz was still set at the default (that was the password causing the error) I changed the password to match and saved it. It seemed to fix the issue with the authentication errors and invalid password. So far, even after a phone restart it connected on its own. Previously had to manually connect it every hour or so.