Here we have four possible readings, at least in theory: “all kind of afflictions” (the earliest extant reading), “all kinds of afflictions” (starting with the 1852 LDS edition), “all kind of affliction” (starting with the 1874 RLDS edition), and “all kinds of affliction” (which has not appeared in any edition). But as explained under kind in Merriam Webster’s Dictionary of English Usage, the singular kind in the expression “these/those kind of ” has a long history, with examples dating from the 1500s, including this one from Philip Sidney (1595): “those kind of objections”. Another example is found in the King James Bible (1611): “and I planted trees in them of all kind of fruits” (Ecclesiastes 2:5). Such usage continues in modern English, including my own speech and writing.
Elsewhere in the Book of Mormon text we have three examples of “all kinds of X”, where X is either a mass noun or a plural count noun:
These examples imply that kind in Alma 20:29 could be an error for kinds and that Oliver Cowdery in his copying for the printer’s manuscript accidentally omitted the plural s. There is one example in the manuscripts which suggests that Oliver favored “all kind of X”; in this example, he initially wrote in 𝓟 “all kind of wild animals” instead of “all manner of wild animals”:
Here the occurrence of the singular kind in the initial reading (“all kind of wild animals”) may have been influenced by the singular kind in the immediately following phrase, “of every kind”.
But there is stronger evidence that the singular kind can occur in these sort of plural contexts:
In this case, the 1911 LDS edition emended the singular kind to the plural kinds. But this example argues that in the original Book of Mormon text the singular kind is possible in plural contexts. The critical text will therefore restore the singular kind in Alma 20:29 and in Ether 9:18.
No matter whether kind or kinds is the original reading here in Alma 20:29, we can have either affliction or afflictions. With the singular form affliction, we have a mass noun; with afflictions, we have a plural count noun. The issue here is whether a plural s might have been accidentally added to affliction during the early transmission of the text. But as already discussed under 1 Nephi 16:35, Mosiah 7:23, and Mosiah 9:3, the critical text will in each case let the earliest textual sources determine the number for the noun affliction(s). The example from Ether 9:18 supports the original use of the plural count noun with the singular kind, in this instance animals (“many other kind of animals”). In addition, there are nine examples in the text of the phrase “all manner of afflictions”, but none of “all manner of affliction”. Thus other examples support the plural afflictions here in Alma 20:29.
Summary: Restore in Alma 20:29 the earliest reading, “all kind of afflictions”; the use of the singular kind in this construction appears to be intended here, especially since there was originally an example of this same nonstandard usage in Ether 9:18.