Contradiction with 1 Chronicles 20:8
The contradiction lies in the claim of lineage or ancestry, as 1 Chronicles 11:42 does not mention Lahmi's brother in 1 Chronicles 20:5.
1 Chronicles 20:8: These were born unto the giant in Gath; and they fell by the hand of David, and by the hand of his servants.
Contradiction with 1 Kings 9:20
The inconsistency is found in the reporting of enemy groups, where no mention is made of the enemies from 1 Chronicles 11:42.
1 Kings 9:20: [And] all the people [that were] left of the Amorites, Hittites, Perizzites, Hivites, and Jebusites, which [were] not of the children of Israel,
Contradiction with 2 Samuel 21:20
This verse contradicts 1 Chronicles 11:42 by offering a different perspective or number related to the giants encountered.
2 Samuel 21:20: And there was yet a battle in Gath, where was a man of [great] stature, that had on every hand six fingers, and on every foot six toes, four and twenty in number; and he also was born to the giant. [the giant: or, Rapha]