I don't react to many FODMAPS. I do react to peppers, celery, garlic and onion if I ingest them. I am OK with them flavoring something and being removed. I'm OK with everything else. OK by - no reactions, everything coming out alright, no extra gas or anything.
I haven't had an upper or lower endoscopy so I have no idea how bad the damage is, but from what I understand of my own body, things are pretty bad in there and I'm not getting all of my nutrients and nutrient dense foods like those I listed are really hard for my body to break down. Right when I started showing severe signs of celiac, I began reacting to MSG and those foods. I've been able to eat everything else just fine.
FODMAPS is definitely something to consider. If it is FODMAPS, you generally will react positively within 2 weeks of being on a low FODMAPS diet. It won't fix everything, but you will see positive results sooner than just going GF.
Corn is definitely also a trigger and it is tough as nails to root out. It's in everything from food packaging to disposable plates and cups, toilet paper, cosmetics etc. It's literally in 90% of anything GF, unless people making the product know work-arounds.
Due to corn being a subsidy in many countries (esp the US!) it's in so much stuff you almost can't get away from it and hospitals do not know how to handle a corn allergy. Its even in saline solution you get in your IV.