The 1840 edition dropped the all here after upon, perhaps because of the all in the immediately preceding phrase, “all the people”. The shorter reading without the all was maintained in the RLDS text until 1908. The 1920 LDS edition deleted the all, probably because the 1840 edition did. The change in the 1920 edition was intentional since it was marked in the committee copy. (See nearby under Ether 13:26 for another case where all was omitted from this same phrase, but in the 1905 LDS edition.)
We note here that there are other passages with a similar repetition of the universal quantifier all:
This last example has the very same phraseology that Ether 13:31 originally had (“all the people upon all the face of the land”). The lack of variation in Ether 15:12 suggests that the 1840 change in Ether 13:31 was a typo, yet in this case the editors for the 1920 edition decided to follow the 1840 edition. Clearly, the original all in “upon all the face of the land” should be restored here in Ether 13:31.
Summary: Restore in Ether 13:31 the all that was accidentally dropped in the 1840 edition (and later followed by the editors for the 1920 LDS edition).