I went through a similar thing with my son. The best part was when an acquaintance recommended the “easier on the stomach” variant of one of the popular formula brands. I checked the box, first ingredient: corn syrup!

For what it’s worth, it’s very hard to be sure switching brands is the causation of a better outcome vs just a correlation. Babies change rapidly so it’s possible that unrelated development is there true source of recovery. But it was definitely a dramatic difference for us exactly when we switched formulas too.