Unless it was a calorie bomb salad, you probably didn’t eat enough. With omad, you need to eat as close to your tdee goals as possible. It’s on just one meal a day, it’s all your meals for the day in one sitting.
My tdee is 2200, so with a deficit, I eat anywhere between 1200-1800 cals, usually in the 1350-1600 cal range. If I were to eat it like a regular meal, that’s only between 675-800 calories, which isn’t sustainable and would have negative long term affects on my body.
The reason why you were successful at 16:8 is because you were probably eating a lot more while still being at a deficit. So, you were able to maintain your 16:8 schedule a lot easier.
But don’t do something just because it works for others. If you can’t do omad, don’t do it. If your max is a 19:5 schedule that you can maintain, that’s better that trying omad and struggling. Keto is great, people have lost so much weight on it paired with IF. But I just can’t do it. I tried and it’s too restrictive for me, but that’s ok. What I do works for me just as well, but maybe not as fast.
As far as being stalled, 18:6 could help. Maybe you need to adjust your tdee for your new weight. Maybe it’s just a normal plateau that you’ll get over in time.
What was in that big salad? Was it like a Cobb salad with meat and cheese and beans, or was it just like a lot of lettuce and tomato? Because I’ve been doing OMAD for nine months, but I wouldn’t last the night if all I ate was lettuce and tomato. You have to eat a filling and nutritious meal with a good amount of protein and fat.
In summertime I will absolutely eat a big salad for OMAD — but it will have sliced grilled chicken breast, a sliced hard boiled egg, chickpeas, and sliced avocado, along with leafy greens, tomatoes, carrots, other green veggies, plus a homemade olive-oil vinaigrette dressing. It can actually get pretty high-calorie.