Hi!
To me it seems as if the roots of all the Effenbergs and Effenbergers are in former Silesia and maybe Bohemia, which are today part of Poland and Czechia.
It sounds as if there should be a geographic origin of the name, but I cannot find any place or hill called "Effenberg".
Maybe it has been a small place and has a polish or czech name today and nobody remembers its former name.
Best regards,
Harald