Are you doing all this from the same domain, say localhost? The only times I’ve seen this happen is if the state value you’re sending to Auth0 isn’t a string. If so, the issue isn’t with the hosted login page, but with your application. The state is generated by your application (in this case I assume by Auth0.js) and is used to prevent a variety of attacks. If it changes between your app starting the auth flow and receiving the callback from Auth0, it’s actually a good thing that login fails.
On GitHub, some folks seem to be having the same problem, also because of an issue with the state not being a string: https://github.com/auth0/auth0.js/issues/655.
I’d try to clear LocalStorage first to see if that fixes the issue. You can also use a incognito window or different browser to debug without having to clear it. If that doesn’t work, switch the hosted login page back to default, to rule out if that really isn’t the issue.
It’s hard to help out more unless you can share your stack with us. So what are you working in (React, Vue, etc), what code are you using to start the auth flow, what browser are you using, etc.