Lipase comes in stronger and milder forms. If you are using the stronger form, try the milder or less of the stronger lipase. Buttermilk is already cultured and acidified. I think that would make getting the correct PH for the mozzarella to stretch properly much more difficult. What type of milk are you using? The couple times I have made mozzarella I used whole Jersey milk and it was delicious, even without lipase.
Susan