The plural afflictions appears to be the correct reading here. Scribe 2 of 𝓟 initially wrote the plural afflictions, then immediately erased the plural s, perhaps because he expected the singular. But he soon decided that the plural was correct, probably when he looked more closely at the original manuscript. In any event, he overwrote the erased s with another s. All printed editions have maintained the plural form here. Since either reading will work, the critical text will accept the plural afflictions here in Alma 4:15. For further discussion regarding the phrase “the affliction(s) of X”, see under Alma 17:30.
Summary: Maintain in Alma 4:15 the corrected plural reading afflictions in “the afflictions of the humble followers of God”.