The most common reason you get an upset stomach after eating buffalo sauce is due to the capsaicin that stimulates the nerves in your stomach and your intestines.
As a result of the irritation in your stomach and intestines from the capsaicin it can lead to a burning sensation and irritation.
The irritation in your stomach and intestines from the capsaicin can cause symptoms such as abdominal pain, nausea and diarrhea and it's often more likely to occur in people with sensitive stomachs or people with pre existing GI issues.
Some people are more sensitive to the capsaicin than other people and if you have irritable bowel syndrome or dyspepsia you can be more prone to negative reactions from the capsaicin.
Other ingredients in the buffalo sauce such as oils, artificial ingredients and stimulants can also lead to digestive issues in some people.
You can also get an upset stomach from other spicy foods as well due to the capsaicin which is a chemical that triggers a specific receptor which can cause a burning sensation.
Or if you eat too much buffalo sauce or hot sauces or spicy foods it can also lead to a stomach upset and even diarrhea.
The capsaicin can also slow the rate at which food you eat exits your stomach and causes the food to sit in your stomach for longer times.