When copying from 𝓞 to 𝓟, Oliver Cowdery changed the plural murmurings in 1 Nephi 16:25 to the singular. Generally, the plural is the expected number for the count noun murmuring, as in the two other nongerundive cases of murmuring(s) in the Book of Mormon:
So there is nothing exceptional about the original plural reading murmurings in 1 Nephi 16:25. (For discussion of the gerundive use of murmuring, see 1 Nephi 17:2.)
Summary: Restore the plural reading of the original manuscript in 1 Nephi 16:25 (“because of his murmurings”); here murmuring(s) is used as a count noun and elsewhere the text favors the plural murmurings over the singular murmuring for such count noun uses.