I just got a hold of the v3.0 boards and found them to have major design flaws. The Tx and Rx pins has been moved up by 1 place toward the DIR pin. This means that the driver board does not connect to the skr 1.3 board UART pin.
My fix was to de-solder the 2 x 1K resistors and the SP pin on the driver board:
and to add a jumper to the SKR 1.3 board as in the picture: