As you eat fewer carbs, your body produces less insulin, and glycogen stores get depleted, of which, your kidneys excrete water and electrolytes like sodium, zinc, magnesium, potassium and iodine in large amounts, causing nutrients deficiency.
On the other hand, Many people who are new to the ketogenic diet don't replace the calories they would usually get from carbohydrates with healthy fats and protein. This leads to a drastic calorie deficit , therefore, your body spends less energy on non-vital systems such as hair growth.
Make sure you compensate your micronutrients loss, or you can balance of gut bacteria by consuming probiotics, it helps better digestion for your body to absorb the nutrients. Or alternatively, you can try to apply coconut oil and Massage your scalp to promote blood flow and hair growth.