Its quite frustrating there doesn't seem to be one definitive answer to the dutch roll question. My understanding was that it was caused by stronger lateral stability and relatively weak directional stability. Aircraft yaws then rolls due to faster moving wing plus increase projected span on the outer wing, the tailfin then acts like a wind vane yawing the aircraft back to zero slip this then causes secondary roll, the aircraft rolls beyond zero slip in the opposite directon and the process is repeated. Also at play I thought was the dihedral effect of the lower wing increasing lateral stability.