There are three occurrences of again in this last part of Mosiah 10. In two cases, there has been a minor tendency to omit the again, possibly because there are so many again’s in this passage. In verse 20, the 1858 Wright edition accidentally skipped the again, but this error was not transmitted into the RLDS text. And in verse 21, Oliver Cowdery initially omitted the final again, but later he added it. His supralinear again is in heavier ink, with the ink more evenly flowing than the inline text; this difference in ink flow suggests that Oliver’s correction was done later, probably when he proofed 𝓟 against 𝓞.
One could argue that the manuscript insertion of the final again could have been the result of editing since Zeniff’s people had been tending their flocks and tilling their ground earlier (as described in Mosiah 9:14: “my people were watering and feeding their flocks and tilling their lands”). References to “beginning again” are found elsewhere in the text, with 15 occurrences of began again (the expected word order in English) and 4 additional occurrences of the more unusual word order, again began (the word order in Mosiah 10:21):
Note that two of the examples of again began are found in this same chapter of Mosiah. Thus the corrected reading in Mosiah 10:21, with its unusual word order, agrees with Zeniff’s language earlier in the chapter. The most reasonable explanation for the final again in Mosiah 10:21 is that this again was a part of the original text.
Summary: Maintain the three occurrences of again in Mosiah 10:20–21, including the final one (which Oliver Cowdery inserted later, probably when he was proofing 𝓟 against 𝓞).