My game is running extremly slow, but only on levels 3 and 4. Level 1 and 2 are completely fine, and I can’t seem to find the issue. Could someone please take a look at my code and project files? Please help! 
My project → https://drive.google.com/file/d/1jDnKP5MTlSkhy3UAJEr_TiHexsMQFemu/view?usp=sharing
I ran your project through the performance profiler, and the bottleneck appeared to be in objects (pre-render, effects update). I’m not sure what this part represents, that may be better answered by one of the developers of GDevelop.
However, I did find this was reduced when iceBlock and iceGrass were their original size. And removing the LightObstacleBehaviour from iceBlock helped a bit. Also reducing the original image for these to 32x32 seemed to make a slight improvement. You may want to look at replacing the tiled sprites with a single sprite that’s been repeated in the scene. But don’t quote me on that last one.
Finally, if you run it in preview mode, make sure you don’t have the scene open in the editor. It really slows down the game.
Ok! I will keep that in mind, and try to repair it. Thanks for your answer!