If you are using this moduel form the market place: https://marketplace.mendix.com/link/component/1414
This error means that the user was authenticated with the external party (like facebook/Google etc.).
The data that was returned is used to retrieve the user in the application and if this user is not found the access attempt is logged.
Have a look at setp 14 of the installation and configuration section, the mentioned microflow is used to retrieve the user, adding a breakpoint on this microflow can help in finding a solution.
If you are using something else then please update the question with the module you are using.