(at around 20 mins) When Kovu falls over onto his back to Zira lecturing him on the Pride Landers, Kovu backs up along the bare ground and then starts to sit up, and cowers down again. The background artists forgot to put in the rock that he would be backed up against - his ears flatten against the invisi-rock.
Okapis appear several times in the film. Whilst these animals are native to Africa, they live in dense rainforest, not on the plains where lions are found (and where they appear in the film). They would never naturally encounter lions.
At the end of the movie, when Simba, Nala, Kiara, and Kovu are walking to the tip of Pride Rock the lioness' in the circle number in 13. In the next shot there are 15. And when lined up as the Royalty walk by there are 12.