From my personal experience. I do not do well with IF and low carbs when my bodyweight / BF is too low. My guess is that I may have been spiking my cortisol levels. I actually had issues with high blood sugar which believe it or not corrected when I ate more food and more carbs. I was very lean at the point where I had the most issues, I just realized that there is a point where I am not as healthy even though I am really lean. I had great strength especially pound for pound but my metabolic workouts had tanked.
This is the personal experience of one your mileage may differ.
I agree with Garret a post workout carb up is at least a pound of sweet potato. Small amounts (say 4-6 ounces each) during the day taken with five or six mixed meals would be a good carb up day IMO.