The original manuscript has the plural mists. In copying from 𝓞 to 𝓟, Oliver Cowdery initially wrote the singular mist, but then immediately added the plural s. The 1830 compositor set the singular, and all subsequent editions have continued with mist rather than the original mists.
Elsewhere the Book of Mormon text consistently uses the plural mists whenever this word is preceded by the definite article the:
Of course, whenever we have a preceding indefinite article (a/an), the text has the singular mist:
The probable cause for replacing mists with mist in 1 Nephi 8:24 is the singular mist that occurred twice in the preceding verse:
Summary: Restore the plural mists in 1 Nephi 8:24 since it is the reading of the earliest textual source (the original manuscript); elsewhere we consistently have “the mists”, never “the mist”.