From the quick googling I did at work, it seems that there are different types of starches that digest at different rates. Whole grain cereals are in the slower-to-digest category *and might not get digested fully.

I personally suspect that the process of making oat milk - blending and straining the oats - makes them easier to digest and probably has an impact on GI. So it’s probably a wash.

Wouldn’t the starch break down into an equivalent amount of sugar during digestion?

Did you get a huge flood of emails at the start? That happened to me one time and it was because one of my old passwords got leaked. Buried within the flood of emails was a legit “your password has been changed” email for an account.