Nueby suggests this above:
Redundant DO pronouns are common with todo even if the actual DO follows the verb. Ahora me lo tienes que contar todo. (Butt & Benjamin's example of usage accepted, perhaps preferred, even in Spain.)
Perhaps the direct object pronoun may be employed because "todo" here is itself a pronoun and could be behaving like other pronouns that are used only for clarification, as in "They had discovered it (everything)."
Anyway, it sounds like "lo" is optional here.