Charles Ellicott Commentary 2 Chronicles 20:33

"Howbeit the high places were not taken away; neither as yet had the people set their hearts unto the God of their fathers." — 2 Chronicles 20:33 (ASV)

Howbeit the high places were not taken away. —This is no contradiction of 2 Chronicles 17:6, And further (or again), he took away the high places. There the holy places of heathenism, here those of the illegal worship of Jehovah, appear to be meant.