Contradiction with Joshua 21:27
This verse states that the cities include "Shechem," which contradicts 1 Chronicles 6:63 mentioning "Kedesh" instead of "Shechem" for the children of Gershon.
Joshua 21:27: And unto the children of Gershon, of the families of the Levites, out of the [other] half tribe of Manasseh [they gave] Golan in Bashan with her suburbs, [to be] a city of refuge for the slayer; and Beeshterah with her suburbs; two cities.
Contradiction with Joshua 21:28
Differences in city listings; this verse includes a city not mentioned in 1 Chronicles 6:63 specifically for the Gershonites.
Joshua 21:28: And out of the tribe of Issachar, Kishon with her suburbs, Dabareh with her suburbs,