itch.io

I got the lag as well and it looks to me like it's a shader compilation issue since it only happened the first time an effect, like an explosion, was shown. The same thing happens to my Godot projects. The web exports tend to make the issue a lot more noticeable.

If it is shader compilation lag, the easiest way to fix it is to have a splash screen at the start of your game covering the screen while you load a scene with one of every material in front of a camera for one frame. That forces Godot to pre-compile all the shaders before the game actually starts (I did the same for my game; although I missed one material). The Godot docs have a more detailed page on why this happens too.