Did Edom make an additional rebellion?
Radak (21): Even though Yehoram defeated them, they constantly rebelled from under Yehudah.
Radak (21, citing his father): (It is not another rebellion.) Jews who fled told Jews in the cities that Edom rebelled.
Malbim: Now they totally rebelled.
'Rashi' (Divrei ha'Yamim II, 21:10): Since a verse interrupted in between, it was repeated.
Who lives in Livnah?
Rashi: I do not know what nation they are from. It is from Eretz Yisrael! I say that they were from Shevet Yehudah, and rebelled against the king. 1
Radak: It is part of Edom. Even though it already said that Edom rebelled, Livnah was closer to Eretz Yisrael than the rest of Edom. When Edom first rebelled, Livnah did not. After this war, Livnah rebelled. This is why it says "ba'Es ha'Hi."
Also Malbim says so. Radak - I find this difficult.
Why did Livnah rebel?
Radak: Refer to 8:22:2:2.
'Rashi' (Divrei ha'Yamim II, 21:10): (They were from Yehudah.) It is because Yehoram "abandoned Hashem Elokei Avosav." Malbim (ibid.) - they wanted a king who follows Torah.