For me I had to find the specific things creating those effects, figuring out the ingredient and portion size.
certain food from a specific cafeteria has that effect on me, whereas other seemingly identical foods don’t: finally I think it is carbohydrate-rich, high salt, or “good” food in a too-large-portion-size which makes me feel how you describe.
perhaps a bit of trial and error to see what the triggers are for you?
Considering that you’re on 16:8 why don’t you experiment having a very light meal after your fast, such as soup or salad, and then, later on, something more nutrient-dense. As a tiny introduction to your body, and it gets your digestion started.
Avoid carbs, eat mainly protein and good fats. No sugar.
I’ve noticed that as well. As I’ve only started three or so weeks ago ( and GENUINELY feel better for it) I figured, as a lifestyle habit I’m fully adopting, I’m just going to iron it out as I go. Aiming for lighter meals and just better more wholesome food.