Here in the printer’s manuscript, Oliver Cowdery initially started to write an s at the end of affliction, with the loop at the top of the s just starting, when he suddenly aborted his partially begun s but without either crossing it out or erasing it. This aborted s definitely suggests that Oliver initially intended to write the plural afflictions in 𝓟, but then he changed his mind in favor of the singular affliction. The 1830 typesetter, however, interpreted the partially begun s in 𝓟 as a bona fide s; thus the 1830 edition and all subsequent editions read with the plural afflictions. Most probably, the original manuscript (not extant here) read in the singular, yet even that might have been an error since Oliver sometimes failed to add the plural s as he took down Joseph Smith’s dictation, as in the following example from 𝓞 where Oliver initially wrote down the singular instead of the correct plural afflictions:
Here in the book of Mosiah there are some other examples of affliction(s) conjoined with famine or modified by sore:
These examples show that except for the one example here in Mosiah 9:3, the book of Mosiah favors the plural afflictions. But elsewhere the text favors the singular affliction in the immediate context of sore or famine (providing there is a choice in number):
So for the whole text, we get variation for affliction(s). This variation argues that in each case the earliest textual sources should determine the number for affliction. Therefore, the critical text will accept the singular affliction in Mosiah 9:3. For further discussion regarding the variation in number for affliction, see under 1 Nephi 16:35.
Summary: Restore the singular affliction in Mosiah 9:3 since the plural s was aborted by Oliver Cowdery as he copied from 𝓞 into 𝓟; here 𝓞 most probably read in the singular; usage elsewhere in the text allows for variability in the number for affliction.