Citristrip? Not surprised it doesn't work for that.
Its pretty good for taking the last coats of varnish or paint off of wood. Much slower, but when working a large area like a floor that's actually an advantage. Pick it up using woodshavings a few hours later or the next morning. Then wipe down.
When I run into some crusted up grease, and the green or purple doesn't work, sometimes fuel works. Failing that, engine foam or uncoat remover. I don't know what's in that undercoat remover but it really cuts through when other stuff won't.