Hmm, I don't know, man. That's a real puzzle right there. Everything is so different for each individual. Zoe seems to think you are eating too little, which you seem to agree with. I eat about 1,750 a day and burn between 400-800 through exercise alone and don't deduct that from my total calories and that's worked out well for me.
I know this is something you've been working on for many years, and I can see it must be incredibly frustrating. I'm no R.D., but are you tracking your nutrients? Making sure that you are hitting the spots you need to hit in regards to essential vitamins and such?
I say this because, to my layman's understanding, malnutrition is a major risk for the severely obese (Not adding you to that list, of course, but using it as an example). They may ingest 4,000-5,000 calories in a day but it's all junk that doesn't sufficiently nourish their bodies.
If you aren't getting proper nourishment, making sure you get all the vitamins and minerals you are supposed to be getting, even with all the exercise and calorie limitation you want to do your body may still enter "Starvation mode" because it's starving for proper nutrition and it will hold on to every bit of nourishment it can get ahold of to try not to start feeding off of itself.
https://en.wikipedia.org/wiki/Starvation_response
I hope I'm not passing off bad science here. As I say, I'm just a layman and as such my understanding is very limited of such an especially complex subject. If my understanding of the science holds true, though, perhaps you aren't losing because despite watching how much you eat and living an active lifestyle the foods you eat aren't providing proper nourishment? I'm totally not trying to sound all "bro-sciency" here or like I know really what the fuck I'm talking about, just trying to relay what MAY be the case.
Just a thought, freind. I wish you luck and, if you aren't already, perhaps consider a multivitamin or something to that effect?