Ahhh okay, it's not exactly a bug, but the effect is displaying a texture page from the game, because some texture is not associated with the effect. I'm not sure which texture exactly, though... This didn't happen before, so either a GM update did this, or some texture is set incorrectly. Could you check if the textures for the effect are defined correct, and not defined to something like -1?
Viewing post in Sketch (Cartoon) Shader [Post-Processing] comments
As far as I can see all textures seem to be defined correctly: https://imgur.com/a/PLQpVf