In this passage we may wonder about the word order after the initial adverbs thrice and twice. Based on the earliest textual sources (the 1830 edition and the printer’s manuscript), which agree here, we have the noninverted word order in verse 21 (“and thrice they were cast”) but the inverted word order in verse 22 (“and twice were they cast”). The RLDS text, beginning with the 1874 edition, switched to the noninverted word order in the second case (“and twice they were cast”), thus making the word order agree in both verses.
Undoubtedly, the mixed order occurred in the original manuscript. Still, one wonders if the first case might have been an error in the original manuscript—that is, perhaps the original text read with the inverted order (“and thrice were they cast”) and that somehow the word order got mixed up during the dictation of the text. There is some internal evidence favoring the inverted word order when the initial adverbial phrase tells us how many times something happened. We have only four other examples in the Book of Mormon, but each of these has the inverted order:
But usually we get variability in word order for cases where there is an initial adverbial phrase; that is, for any particular adverbial phrase, either word order, inverted or noninverted, is possible. For an example, see the case of the sentence-initial “and then” under 3 Nephi 5:17. Since either word order is generally possible, the critical text will accept the variability of the earliest reading here in 3 Nephi 28:21–22, namely, “thrice they were cast” in verse 21 but “twice were they cast” in verse 22.
Summary: Maintain in 3 Nephi 28:21–22 the noninverted order in verse 21 (“thrice they were cast”) and the inverted order in verse 22 (“twice were they cast”); these are the readings of the earliest textual sources (𝓟 and the 1830 edition) for this passage.