It seems there are some inconsistency in the formation energy of sulfides and fluorides.
For example, the formation energy of Li2S is -4.681 eV (-1.56 eV/atom) in reaction calculator, but is -1.339 eV/atom in mp-1153. This problem is noticed for fluoride also. Similar search on oxides and others would give consistent results.
It seems that the recent S anion correction is not included for the formation energy in the sulfide at the MP entry pages.