Here are some of the clues:
The low FODMAP diet didn't result in any improvement in my symptoms.
I eat cabbage, onions, apples, cantaloupe, and mangoes without any problems.
My symptoms are all about systemic inflammation (brain fog, bradycardia, long GI transit time, sore muscles, poor sleep, and need to sleep as much as 12 hours per day).
I had a cup of the bean broth from cooking beans while in Honduras and my GI tract was very uncomfortable in the hours afterward.
I discovered that rinsing beans after cooking was critical for being able to eat beans.
I ate some organic string beans and reacted strongly.
My reactions to beans led me to realize that it was something in the skin of the beans that was causing my problems and that led me to investigate saponins. I discovered that I had developed a low saponin diet by trial and error and gradually realized that the remaining foods in my restricted diet that were causing problems all had higher levels of saponins.
I'm still figuring this out. But given the known connection between saponins and leaky gut I've wondered if there might be others in the IBS community who are struggling to find a diet that works and might find that the problem could be saponins.