Sticky Pistons with Slime Blocks Duplicate Attached Blocks

Using the 3x3 trapdoor designed by Youtube channel 'Mumbo Jumbo', every time I activate the redstone, two spruce planks are created, and it does this for seemingly infinity.

However, it doesn't do this all the time. And when I reloaded the world, the duplicated blocks were gone.

I used the exact same design from the video, but I added an XOR gate to close the trapdoor behind me.

Trapdoor design:
(https://www.youtube.com/watch?v=s8a4ERfFQyM)