I kind of doubt that it has anything to do with IF, but it’s definitely possible to develop food sensitivities/allergies as an adult. I developed an egg allergy in my early 30s - even a small amount of egg in a baked good would give me the worst stomach cramps and diarrhea. Lasted about a year, then it went away and I can eat eggs just fine now.
I know a couple people who are allergic to avocados - I think that is a fairly common sensitivity. Maybe just try taking a break from it for a few months and see what happens.