Hyrum Smith originally wrote men, then almost immediately overwrote the e with an a. His initial men was probably influenced by the plural men that occurs within the following sentence, in verse 13: “that ye could have just men to be your kings”. The singular man is consistent with the two preceding occurrences of man in this passage. Either reading would theoretically work in “the judgments of man/men”, so there would have been no motivation for Hyrum to have consciously emended the text here. The critical text will therefore follow the corrected reading in 𝓟, the singular man.
Summary: Maintain in Mosiah 29:12 the corrected singular man in 𝓟: “but the judgments of man are not always just”.