I don't really agree with the OP, but I do think there is at least one, possibly two such examples. The pretty clear one is nutrition: the vast majority of studies and recommendations made over the years are pure bullshit, and quite transparently so. They either study a handful of people in detail, or a huge swathe of population in aggregate, and get so many confounding variables that there is 0 explanatory power in any of them. This is quite obvious to anyone, but the field keeps churning out papers and making official recommendations as if they know anything more about nutrition than "missing certain key nutrients can cause certain disease, like scurvy for missing vitamin C".