Login problem

I have a Fluent Forms form set up, which is integrated with Fluent Community and after filling it out, the user creates an account and logs in to Fluent Community.
However, when the user logs out of the account, they cannot log in again and it says that they entered the wrong name or password - even though they entered everything correctly.
Only when I, as the administrator, open the WordPress user in the administration and set their password (the same as they entered when registering) again, does the login work for them.
Why?

I have integration only with Fluent Community... Do I also need a separate integration for WP User Registration?