I buy freshly-made pasta from Whole Foods (Marin Pasta Works pappardelle). I put 20 oz pasta in 2 quarts of water. I stir vigorously the second the pasta goes in. But even then, some strands - 5% - stick together. The only way to unstick them is to pull them apart with my fingers.
Then after draining and sitting for a couple minutes, 100% stick together.
Maybe after draining I should rinse with hot water (from kettle)? But that still won't fix the 5% that are stuck from the beginning.