Hello, Geni Support team.
I'd like to point you to the bug with the Geni Consistency Checker. The type which seems to work incorrectly is "the Children With Different Last Names inconsistency". I've got errors by this check for children which are married and changed their surname, so their father has the last name similar to their birth surname, but their last name now differs from the last name of the parents.
But your check works as mentioned: "The Geni Consistency Checker will report "Children with different last names" on any profile that has one or more children whose last names appear to not match the parent, when it should." Is the birth surname taken into account?
And one more nuance is possible differencies in the spelling of the surname's ending for heterosexual relatives, as example - "Васильев" for man and "Васильева" for woman - that is the same surname in Russian.
In case you have any questions to clarify my point of the bug feel free to ask.