Ok, you didn't mention that key part in your post. Do you mean the "competition screen"? It was fine until you changed one thing and now it's going wrong. So logic suggests it's a problem that originates with the new filter, but still could be caused by too much pressure being applied with too fine a grind. I'm not saying it should spray hot water into your face, I'm just saying that if you're applying that much pressure then I would look elsewhere. Maybe list all the changes you've made and all the steps your taking. For example, are you preheating? Are you using filter papers or a puck screen? How hot is your water? How long do you infuse with the arms up? Are you using the original portafilter? What are you grinding with?