Both thesis and antithesis seem true. Perhaps it is the fact that we are constrained by experience that entangles us in these intractable questions. The fact that the causation involved in free action is beyond possible experience does not mean that the idea of such a causality is meaningless. Experience is not the best guide in other respects, as well. An effect can be caused by many causes or many causes can lead to the same effect.
Experience also involves mnemic causation rather than the conventional kind.
In the former, the proximate cause is composed not only of a current event but also of a past event. The past cannot have a direct effect without such mediation. Russel, on the other hand, rejected this and did not refrain from engaging in what effectively turned out to be action at a distance. This is not to mention backwards causation. A confession is perceived by many to annul past sins.