I have had Gastritis for about a year or so, prior to HypoT/Hashi diagnosis. I believe I have read that since the thyroid helps regulate the rate of digestion, food can stay in the stomach longer than usual, and can cause issues. I'm not sure which issues would be likely from thyroid disorders, and which not.
I would just guess bloating, gas, and of course, constipation. Not sure about my gastritis, or your UC.
My opinions only, not medical advice. Always follow advice of your Doctor, not what I say here.