Old topic, similar problem. After some of my guests complained about lack of internet access through the Portal, I found that they were trying through the Google app, which requires logging in to their Google account before anything else happens.
Either they didnt have a separate browser installed, or if they did, they didnt know how to use it.
If they had Chrome, that worked OK.
On this subject, I get a lot less problems reported using the username only for logging on. That is enough to keep out the casual leachers, which is all I care about.