My surgery for SCC (not HPV) involved ear and neck but just prior to surgery I developed a metallic taste in my mouth. It was because of the tumor invading the facial nerve. Once that section of nerve was removed and the nerve ends reattached, I had total facial paralysis of that side for many months/years. I was undergoing radiation at the time also so taste changes continued/worsened. Taste never went back to normal completely but metallic taste is long gone. I wonder if there was irritation or damage to part of your facial nerve during the lymph node dissection? Nerves are very slow to heal, so improvement could be quite delayed. I am still finding nerve changes over 11 years since that original surgery.