Collision stopped working on copy-pasted objects?

Here's what I did, in order:

1. Created a boulder sprite.
2. Created a "boulder hitbox" sprite and stuck it right on top of boulder
3. Set the boulder hitbox sprite to Qualifier 4 and unchecked "Visible on start"
4. Event editor: "When player collides with Group.4, player stop"
5. Tested the boulder, everything works as intended
6. Copy-pasted a bunch of the boulder+boulder hitbox and stuck it everywhere

But then the player glides through the other boulders. The original still works, but none of the copy-pastes do. They're all still part of Group.4 and I deslected "Destroy if too far from frame" and also "Deactivate if too far from window". Any ideas?

Omg thats got to be it! I cant actually check until monday but im positive youre right. Thank you so much!

Yup, in case anyone was wondering, layers were the problem. Thanks all!