"Screen" from different package fails to load narrator and crashes

[themg95]

I have a package in my project called "ui" and it has a few classes that extend Screen. For some reason, they've randomly stopped working and now every time I try to open one of those screens the game crashes with:
java.lang.ClassNotFoundException: net.minecraft.class_437
which seems to be the narrator. This error doesnt happent when the Screen is in the same package.