If the user only sees a blank white page after logging in, possibly with the text about missing permissions, the reason is the absence of a group set at the LDAP level. LDAP or another external user data source is considered the "point of truth" from which the user's permission level is taken. If a user has no group set up in LDAP, they have no permissions in ANT ID either.
In this case, the user needs to be added a group at the LDAP level (or other external source). After the refresh, the permissions taken from the defined group will already be taken into account and the user will see the relevant functions in the application.