Are you also eating low carb? Poor sleep is a fairly well-documented side effect of that and I’ve definitely experienced it. What has really helped me is to eat carbs about an hour before I go to bed (I almost always eat oatmeal with some peanut butter and bananas in it). I shifted my eating window specifically to allow for that and now I sleep great. I also take L-Theanine and L-Ttyptophan at night and that helps me too.
Generally speaking though, IF and being on a caloric deficit can increase cortisol levels which affects sleep.