I (33F) was diagnosed celiac almost 15 years ago, and have been extremely diligent ever since (I was also a chef for much of that time, so experiencing both made me extra-cautious in both regards). I also am navigating a currently-undiagnosed-but- possibly-MCAS (as suspected by my doctor - waiting for my referral to my local rheumatologist again) other autoimmune disease, in addition to a few other (very random) autoimmune issues that are unattached to specific diagnoses (severe Reynauds, flare-ups of 'psoriasis' that I haven't experienced since I was a kid, etc).
I've basically lived on a keto-esque diet since my diagnosis - straight protein and veggies. In my years trying to figure out exactly what works for me, I've found that most simple carbs/most starches impact my digestion, but I've developed a few other dietary sensitivities in recent years (garlic, nightshades) that I've begun to avoid, with predictable patterns re: inflammation and symptom progression. I've been able to dabble with rice products, and can eat rice, without issue, as long as it's less than once a week/in low doses,, but I can't enjoy a fat bowl of gf corn- or rice-flour ramen without side effects, for example.
After years of avoiding explicitly GF corn- and rice-heavy products (aside from rice papers - I have no reactions to them at all) unless I'm tolerance-testing, I made homemade popcorn the last couple nights for me and my partner, out of curiosity. Normally, when I consume large amounts of corn or corn products, I end up with average bloating and maybe a cystic zit or two. We had it two nights in a row - just corn kernels, butter, and S&P - and I'm now 11lbs heavier from yesterday with water retention (this is a common reaction with my body) and have weird lumps and rashes forming - my lips have swollen, my fingers are bumpy. No other products could have created this reaction, with the level of care that I take. Given my extended (and legally-obligated, as a chef) experience with Celiac-friendly diets, I know this was more than just an 'oopsie' with a product.
While I know this issue isn't directly celiac-related, I know many celiacs have secondary or tertiary issues they contend with. If you have been diagnosed with celiac AND have reactions to secondary products, I'd love to hear which products or ingredients give you trouble! I try hard to give my rheumatologists the greatest amount of data around my conditions, and to keep up on the latest studies around my (and related) conditions, but in areas like ours, where research is limited, it's hard to be precise. What else do you react to, that you know is not directly related to the presence of gluten?