Acrid bitterness

I am a relatively new brewer. I helped a friend for some years with good success. My first six brews (all chocolate porters) were delicious. Each was a mix of chocolate grains and amber extract. Then, i changed the recipe a little to increase alcohol and reduce hop flavor and the next one had a harsh, acrid bitterness on the back of the tongue. I threw that batch out and tried another. Same result. I read in this forum about water, cleanliness and hop balance. I got anal about cleanliness, went back to original recipe, and bought a new filter for the water. Still same result. Tried an all extract amber recipe from on-line source with same result. Anyone have any other ideas ? Could it be burt flavor from extract syrup - there’s always a little on the bottom of the kettle - same with two different kettles.

What temperature are you steeping your grains at? If it’s above 170* you could be tasting off-flavors from that.