I managed to get it to work in your code. I had a similar issue once and it took me ages to find out what was wrong or what I think was wrong.
A couple of things first, I'd suggest that you name your collision layers, that way it's easier to see what an object is colliding with.
You have large asteroid on layer 3 and the small and medium asteroids on levels 2 & 3. I'm guessing they all need to be on level 3.
The player mask is set to the same as itself, so I think the mask needs to 3, to collide with the asteroids.
Now the reason I think you are having issues, (this is a bit of a guess) is that you may have copied one of the asteroids to make the medium or big one and something in Godot doesn't like it.
I deleted your middle asteroid and recreated it from scratch and added the script as a file and it works fine.
Here's the code