You don’t have to, but you likely have more than 3 (which the secondary voltage transformer would be in phase with) circuits on the other phase in your panel. Cuttings those jumpers splits the voltage input from the barrel jack on the main board from going to the other side of the meter (channels 4-6). With the add-on board, it’s also split if you sever the jumpers, but unless VA2 is hooked up to the second transformer they will not get a voltage reference.
So, for example, if you want the left side current channels (in your case 9) of all the boards to reference the voltage connected to the barrel jack, and the right, the secondary voltage, cut all of the jumpers, then connect the secondary voltage transformer to all of the VA2 pins. Do not connect the barrel jack and VA2 on the same board without cutting the jumpers!