Not enough calories on your eating days. Try 3000 calories on your eating days for a week, then 2000 the next day. You can’t eat that few calories consistently without your body “forgetting” how to burn them. Also, that kind of consistency is the problem. Shake things up. When you get back to low calorie eating days make sure to throw in one high calorie eating day per week. Keep your body on its toes.
Don’t overthink it. If you are fasting every other day you ARE burning fat, even if it doesn’t register on the scales. You should expect to lose approximately 1 pound every 4 days, doing what you are doing. If your weight loss stalls, it is likely down to fluctuations in water weight, and water weight can fluctuate massively; for example, I am on average 5lbs heavier in the evening than in the morning because of this. Even if you haven’t lost weight according to the scale, you might have simply lost 2lbs of fat, and gained 2lbs of water.