I think the issue is that the user account creation screen does not trim spaces off user ids, but the login screen does. That happened to me a few years back.
So once you create a user id with a trailing space and log off, you cannot log on as that user, using the web page. I think some of the phone apps allow you to sign on with a trailing space. The whole scene is quite confusing.
Hope this helps to understand the potential cause even if it isn’t a solution.