Check out a quick video in the link bellow.
https://photos.app.goo.gl/8RVNmLtoGAXuQYiv5
There's a chance the pins just aren't making good contact in the Arduino. One way to solve this is to, like you see in that video, put a very slight inwards angled bend into the pins of the SpikerShield. I lever the SpikerShield against a table to gently bend the pins inward, mate it with the Arduino (ensuring all pins are in!) and the once it is pressed in, pull up just slightly on the shield.
Make sure the needles go to the end and to be pressed firmly. If it is not attached right the signal won't be transmitted.