I have found my people!!! TL;DR - I have a semi-solution and still working on it.

I have this issue too for many years - it started (or I started noticing it) after I had bronchitis in 2015 or so. Afterwards I had air hunger and breathing dysfunction like this and it became permanent. At first I was treated for asthma but the inhaler did not work for these symptoms and so I moved on from that. Then I explored anxiety but - same as you - nothing seemed to correlate with when I would suffer the symptoms. Sometimes I would notice I was breathing normally and as soon as I would notice it, the noticing would make it dysfunctional. It was maddening. I saw an ENT and was treated for GERD, but it did not improve even when the scope showed the reflux had improved (our trajectory is so similar!)
Then I was unemployed for 6 months during lockdown and did a lot of reading. I read The Oxygen Advantage and the wheels started turning… so it seemed I was an overbreather and my body had developed a low CO2 tolerance?
I was just beginning down the path.
Then I read Breath by James Nestor.
This put together a lot of puzzle pieces for me — it discussed the issues of mouth breathing vs nasal breathing, and of a narrowed airway in response to retractive orthodontics, which I had as a child (pulling my 4 bicuspids and making my mouth smaller to solve crowded teeth). So, at this point my issue was not solved but I had a fresh Avenue of inquiry. I should mention that I also had chronic tension of the neck, jaw, and shoulders, clenched my teeth at night, and suffered frequent headaches. I learned that these symptoms, as a grouping, can often be the result of the tongue not resting properly in the mouth, in my case from my arch being too small from the orthodontics, and, before that, from a tongue tie that I was soon to be diagnosed with! (Stay with me cause I will get back to the breathing)… these can also lead to a narrow airway. So now I had an Avenue of inquiry that touched on many chronic issues I had had for years and always suspected may be related.

I began seeing Dr Zaghi at The Breathe Institute in LA, and Dr Hang at Face Focused Orthodontics. Both wonderful doctors I am lucky to have in my home city.

I will try to shorten this story by a lot!
I am now mid-way through a 2-year course of orthodontic treatment to completely reverse the earlier orthodontics, broaden the arch, replace the missing teeth with implants, AND have just 2 weeks ago had my tongue tie released.

HERE IS THE RELEVANT PART for y’all:

I did not know what to expect with the tongue tie release with respect to my breathing but I was hoping it would at least release a lot of the tension I had. Then I planned to work on the breathing with my Myofunctional therapist (look it up!) afterward.

The tongue tie release surgery was a WILD experience. With each snip of the scissors my body was shaking uncontrollably but the doctor assured me this was my body releasing all the tension. By the end of the brief procedure, I suddenly realized even my calves and ankles were looser than ever before.
The next day, my entire body felt different — all the tension in my neck and shoulders, down to my feet, was gone. I woke up feeling more refreshed than ever before and did not grind my teeth that night.
The following day …
I realized… wait…. My breathing is totally relaxed, light as a feather, NORMAL. I felt that ability to create full negative pressure on the exhale to fuel a full inhale. It felt amazing.
WOW!
Here is my theory - because I felt this in my whole body - it seemed like my sympathetic nervous system had been elevated my whole life… I always had a hard time relaxing. It felt like someone had finally found the “OFF” switch. The parasympathetic system was able to take over, including the relaxed breathing.

HOWEVER, in the past two weeks since the surgery, my symptoms have been sloooowly creeping back in…. I am clenching again when I sleep… and the air hunger issue has 50% returned. Like I have some ability to relax it and breathe lightly, and halfway it is not in my control.

So: I am still working on these things with my Myofunctional therapist, and trying to figure it out for myself. But in my personal experience I now understand this issue as being a dysfunction of my nervous system…I saw that it could disappear overnight by finding the “off” switch. (As opposed to it being a CO2 intolerance that I needed to gradually re-train).

Feel free to reach out! I understand the struggle.

Would also love to know an update on anyone… Gabriel, Buteyko is definitely a big part of Myofunctional therapy… probably something I will need to dig into in my coming sessions.

Right now I am working on breathing while speaking, as this is a related challenge for me.