That animation is white snowflakes on a blue gradient background, and the gradient is set by a separate cell that provides an html <style> element. The second notebook is importing the canvas, but not the associated style cell, so it’s animating white snowflakes on a white background, so it appears blank.
You can fix this by either naming the style cell, importing it, and referring to it in the second notebook, or setting the style in the same cell as you set the animation, like